See http://www.nps.gov/grte/ for
the Grand Tetons official site.
Note that all the trails are well defined and there are distance to go 
markers at the start and at each trail junction.
Also note that the upper trails may still be snowed over until mid-July 
or later.   There were a number of snow patches heading up and down from
the Paintbrush Divide when I went July 23, but the other trails were
clear.
Wyoming Pictures (16 pictures)
  String and Leigh Lakes
  Directions:
    String Lake-Leigh Lake parking lot
    bathroom with sinks (no water fountain)
    $20 per car for a 7 day pass or National Parks Pass
  Trails:
    2-person or so width, dirt trail that goes along String Lake and 
    Leigh Lakes.  Pretty reflection views in the mornings.
  Trail Length + Elevation:
    Up to 2 miles one-way to end of Leigh Lake (1 mile to Leigh Lake),
    fairly flat
  Area:
    Lower lakes with the Tetons above
  Picture
  When I did the hike:
    July 2003 (couple of times); Thursday, August 28, 2007
  Recommendation:
    Definitely, good for a short hike or family hike.
  Paintbrush-Cascade Canyons loop
  Directions:
    String Lake trailhead parking lot - the first parking lot 
    for the area.
    Bathroom with sinks at nearby Leigh Lake parking lot
    $20 per car for a 7 day pass or National Parks Pass
  Trails:
    For those who want a challenge and to see it all in 1 day, there 
    is this almost 20 mile, 3,845 feet gained monster loop.  For those
    who don't want the challenge, skip the divide and do the 2 lakes
    on separate days.  To start the hike, you can either go below or
    above String Lake - there is little mileage difference between the
    two.  To go below, take the Leigh Lake trail (this is the prettier 
    way) for a mile, cross the bridge, and then after a little bit
    you'll start to gain elevation for almost a mile before joining
    up with the above way.  To go above, cross the bridge near the
    String Lake trailhead parking lot and then hang a right.  The
    one-person width dirt trail starts climbing right away and includes
    an open area from an old fire (green though, not burnt out).  After
    about another mile from the Leigh Lake junction, the trail starts
    heading up into the canyon.  It's a foresty few miles with a
    gradual elevation increase.  Then come some switchbacks and some 
    open and rocky terrain.  After several more switchbacks (not a 
    ton) and rocky terrain comes the junction for Holly Lake.  Take a
    right and you have about 1/2 a mile to go.  Be sure to take a look 
    at the small lake shortly after the fork and take a short a trip up 
    the rocks for a good look down into Paintbrush Canyon.  Holly Lake 
    is a nice sized mountain lake in a half-bowl.  It took me almost 3 
    1/2 hours to get to Holly Lake (only took me 3 hours the 2nd time).  
    Rest and relax at the lake.  If you're lucky, you'll have it to 
    yourself.  If you're heading up the divide, rest and relax some 
    more, 'cause you have a really tough hike ahead of you.  The up
    starts right way heading away from Holly Lake and continues for
    the next 2.2 miles to the divide.  And a little ways past Holly
    Lake, the trail gets rocky - small loose rocks.  Add to that fun,
    in addition to a harder grade, were a good number of snow patches
    (weren't any patches in late August 2007).  There were enough 
    prior footprints through the snow that I didn't need an ice ax, 
    but it was slow going and I put my sun glasses on due to the 
    glare.  It took me 2 hours just to get from Holly Lake to the 
    divide.  But I let out a big "YES" and "Woohoo!" when I reached 
    the divide.  In contrast, it only took me 1 1/4 hours to hike the 
    2.2 miles from the divide down to Lake Solitude.  The views 
    coming down from the divide are the reason to do the loop in this 
    direction as you can see Lake Solitude the whole way down and you 
    get glimpses at the small, precious Mica Lake (no trail to it) 
    [there are no views of Holly Lake until you are almost there].  
    Lake Solitude is a large sized mountain lake - and there will also 
    likely be others there.  Rest and enjoy the lake, 'cause it's a 
    long hike down Cascade Canyon.  I didn't find Cascade Canyon as
    pretty as Paintbrush Canyon, but it does have some pretty views
    of the peaks.  It's a more open canyon with less shade until
    closer to Jenny Lake.  The last several miles are just a trudge.
    After all the scenery along the loop, Inspiration Point (which
    looks out on Jenny Lake) wasn't very inspirational and Hidden 
    Falls were pretty blah.  Including breaks at the lakes and rests
    along the way (many in Cascade Canyon), the loop took me a little
    over 11 hours to complete [started at 7 am, finished at 6:10 pm].
  Trail Length + Elevation:
    6.2 miles, 2,535 feet from String Lake up to Holly Lake
    2.2 miles, 1,310 feet from Holly Lake up to Paintbrush Divide
    2.2 miles, 1,593 feet from Paintbrush Divide down to Lake Solitude
    7.2 miles, 2,252 feet from Lake Solitude down to Jenny Lake
    2 miles, fairly level from Jenny Lake to String Lake parking lot
  Area:
    Lower lakes, wooded areas, open areas, mountain lakes, waterfalls,
    rugged divide.  I saw elk (male, female, kid), moose, lots of
    marmots, squirrels, and chipmunks.  I didn't see any bear, but
    it is bear country.
  Pictures
  When I did the hike:
    Wednesday, July 23, 2003; Monday, July 28 (to Holly Lake and back);
    Thursday, August 30, 2007; Thursday, August 11, 2011 (Holly Lake
    [pass still snowed over with 2011 heavy snow pack])
  Recommendation:
    Needless to say, this is a tough, tough hike and you need to be in
    really good shape to consider doing this in one day.  The many 
    pretty views and sense of accomplishment when you reach Paintbrush 
    Divide are worth it.  If you don't want to do the much harder loop, 
    you can do one-way separate hikes to Holly Lake and Lake Solitude 
    (and take 2 miles off the Lake Solitude hike by taking the shuttle 
    boat (fee) instead of hiking around Lake Jenny).  Both lakes are 
    well worth visits.  I liked the Paintbrush Canyon and Holly Lake 
    better than Cascade Canyon and Lake Solitude and re-did that hike 
    on my last day.
  Lake Marion-Granite Canyon
  Directions:
    Teton Village tram station [note that the tram doesn't start until
    9 am and stops at 6 pm]
    bathroom and food at top of the tram ride
    $15 (non-summer) or $17 (summer) for the tram trip up  [don't need
    a Park pass or park fee unless you park at the Granite Canyon
    trailhead]
    NOTE: The tram closed in 2006, so this hike is no longer 
    possible (unless you want to hike up the mountain, which would
    make it a multi-day hike).
  Trails:
    This hike starts with a steep down as the trail goes down the 
    backside of Mt Rendezvous.  Then you go up the next hill and down
    the other side.  Then a level area for about 1/2 a mile across a 
    plain and most of the rest of the way is open area (little shade)
    to the lake.  After going down and crossing a creek, the trail goes
    up and up and up over a good-size hill.  And then down the other 
    side of the hill to the canyon junction.  Ahead is a steep .6
    mile climb to Marion Lake.  It took me about 3 1/2 hours to get
    from the tram to Marion Lake - I was tired though (did the big hike
    the day before), so most would probably get there quicker.  Marion
    Lake is a smaller sized mountain lake that isn't too impressive.
    I didn't stay too long as the clouds started rolling in - it did 
    rain on me during the hike down.  After Paintbrush and Cascade
    Canyons, the hike down Granite Canyon wasn't very impressive.  
    There were lots of open areas, some tree areas, and occasionally
    the trail went along the stream.  Most of it descends gradually,
    but there were a couple of ups and a couple of switchbacks down.
    It's a long hike from the lake back to Teton Village.  It took
    me about 5 hours to do that stretch, including breaks along the 
    way (again, I was tired, so it was a slower pace and longer breaks).
  Trail Length + Elevation:
    Almost 6 miles from the tram to Marion Lake (lists 1,206 feet gained,
    but I think it was more than that with the ups-and-downs)
    The junction for Granite Canyon is .6 miles before Marion Lake
    About 9.5 miles from junction down to and over to Teton Village
    (includes 2.5 mile connecting trail), 4,135 feet lost
  Area:
    Down and up and down and up and down mountains, small mountain
    lake, woodsy canyon
  Picture
  When I did the hike:
    Thursday, July 24, 2003
  Recommendation:
    Only if you've already down the other Teton hikes.  Lake Marion
    was the least impressive of the mountain lakes I visited - and you
    probably won't be lucky enough to see a moose cooling off in the 
    lake to make this hike worth it.  But any mountain lake is worth 
    visiting.  It's not an easy hike as it's an up-and-down-up-and-down
    hike to the lake and those take more energy.
    NOTE: The tram closed in 2006, so this hike is no longer 
    possible (unless you want to hike up the mountain, which would
    make it a multi-day hike).
  Surprise and Amphitheater Lakes
  Directions:
    In the Tetons, take the Lupine Meadows dirt road to the end.  
    chemical toilet in parking lot, no water
    Note that the parking lot and overflow lots were full when I 
    finished my hike.
    $20 per car for a 7 day pass or National Parks Pass
  Trails:
    The steepest trail in the park is also the most rewarding.  The
    one-person width dirt trail (some rocks higher up) starts fairly
    level for less than a mile and then heads up along a ridge at
    a decent grade for another mile or so.  The trail is in the 
    trees most of the way.  The fun starts as you zig-zag up the 
    mountain.  It starts as long zig-zags and they get shorter the 
    higher up you go.  There are 9 long zig-zags and 8 shorter ones.
    Once they finally end, it is a short mild bit to Surprise Lake.
    Surprise Lake is a pretty, small-sized mountain lake.  A lot of 
    people only made short visits to Surprise Lake or even skipped 
    it all together, but I really liked this lake and even stopped 
    there again on the way back down.  It took me about 2 1/2 hours 
    to get to Surprise Lake.  Amphitheater Lake is only .2 miles 
    ahead, but it's all up.  And it is the jewel of the park.  It's
    a good sized mountain lake and it's got the cathedrals (the 3 
    tallest peaks of the Tetons) looming above.  Go a little above 
    the lake to the left and you might get some stunning reflection 
    views of the peaks on the lake.  Stay a while and enjoy the 
    majesty.  The hike up didn't leave me sore or tired 
    (surprisingly), but the hike down had my legs, knees, and feet 
    screaming in pain (it was my 3rd tough hike in 4 days).  It 
    took me about 2 hours to get from Surprise Lake back to the car.
    The second time I did this hike, I took a sidetrip to Garnet
    Canyon - the junction for that trail is shortly after the 5th 
    switchback of the Amphitheater trail.  The trail goes for 1.1
    miles and ends at a boulder field (rock climbers continue on).
    It is a short up to start and then fairly mild as the trail 
    rounds the bend.  Turnaround at a good view up the valley of 
    the 2 peaks, just before the rock field - continuing will 
    just exert more effort and not give you any better views.
    The trail goes through the rock field, walking on the loose 
    rocks.  There are a couple of switchbacks ahead.  The trail
    ends at a boulder field with no easy way through it.
  Trail Length + Elevation:
    4.8 miles, 2,958 feet to Amphitheater Lake
  Area:
    Mostly tree area, with some open area during the zig-zags, 2
    precious mountain lakes
  Picture
  When I did the hike:
    Saturday, July 26, 2003; Thursday, August 30, 2007 (plus 
    Garnet Canyon)
  Recommendation:
    If you can only do 1 hike in the Tetons, this is the one to do.
    You shouldn't visit the Tetons without doing this hike.  [You
    likely won't have the lakes to yourself, though.  I saw lots and 
    lots of people during the hike.]  If you have the energy, on 
    the way down, you can take an about .5 mile mild sidetrip for
    Garnet Canyon - round the mend and turn around after a short 
    bit (don't go all the way up the canyon).
  Taggart and Bradley Lakes
  Directions:
    Park in the Taggart Lake parking lot
    non-flush toilet in parking lot, no water
    $20 per car for a 7 day pass or National Parks Pass
  Trails:
    It's a fairly easy 2 mile hike along a one-person width dirt trail
    to Taggart Lake, a good sized lower lake.  It's a little bit of a 
    climb from Taggart to Bradley Lake.  Bradley Lake is a little bit
    smaller than Taggart Lake.
  Trail Length + Elevation:
    2 miles, small elevation to Taggart Lake
    1 mile, about 300 feet from Taggart to Bradley Lake
    2 miles back to the parking lot
  Area:
    Fairly open (old 1985 fire area) to the lakes and trees around 
    pretty, lower mountain lakes
  When I did the hike:
    Sunday, July 27, 2003
  Recommendation:
    A nice little hike for an easier day.  If you go early enough,
    you can avoid the crowds and have some pretty mountain reflections 
    on the lakes.
  Ski Lake (Teton Pass)
  Directions:
    From Jackson, take Rt 22 (stop light at Rt 89-22 junction)
    west towards Teton Pass.  Heading up towards the pass, 
    just past a U-curve in the road a little bit before 
    reaching the pass (on the east side of the pass) is a dirt 
    parking area on the left (south) and just past that on the 
    right is turn for a gravel road (which is the start of the 
    hike).
    No facilities.
    Free.
  Trails:
    After (carefully) crossing Rt 22, walk up the gravel road
    (Philip Canyon road) a short bit to the info sign.  
    Continue on the road a little bit and then take a left
    at the sign for Ski Lake on to a packed dirt trail.  The
    trail stays just a little above the road for a ways as it
    heads a mild up.  The trail gets further above the road
    and then heads left into the trees with a bit more of an
    up (not hard).  After a short down, the trail reaches a
    large meadow.  At the end of the meadow is a signed 
    junction - take a left for Ski Lake.  The trail goes 
    through some trees and some meadows as it heads up (again,
    not hard) and over to the lake, a little over a mile from
    the junction.  The small, circular lake was blah, not 
    scenic, smelly, and buggy when I was there (and, thus, I
    basically turned around and headed back shortly after
    reaching the lake).
  Trail Length + Elevation:
    2.5 miles, 850 ft  one-way
  Area:
    Mountains, trees, blah lake
  When I did the hike:
    Wednesday, August 10, 2011
  Recommendation:
    Nope.  Your time is much better spent in Grand Teton 
    National Park.  
  Mammoth Hot Springs area - Yellowstone National Park
  Directions:
    In Yellowstone, in the Mammoth Hot Springs area, there 
    area parking areas in the lower terraces area alongside
    the main road and in upper terraces area shortly on the 
    Upper Terraces Drive (loop).  Park where ever you can 
    find a spot - you'll want to see both the upper and 
    lower areas.
    $20 per car for a 7 day pass or National Parks Pass
  Trails:
    Almost everything is boardwalk and wooden steps as the 
    trails makes its way above and around the beautiful 
    Mammoth Hot Springs terraces.  Pick up a brochure along 
    the way ($1) for more information about the area [grumble, 
    can't find mine].  I really liked the area to the upper 
    south with a pretty thermal spring on top of the terrace 
    and the area to the lower north with a colorful mound.
  Trail Length:
    about .5 mile
  Area:
    Thermal area
  Picture
  When I did the hike:
    September 2006; Friday, August 12, 2011
  Recommendation:
    Absolutely.  A unique area - one of the few terraces
    in the world.  Be sure to also do the Upper Terraces 
    Loop Drive.
  Artists Paintpots - Yellowstone National Park
  Directions:
    In Yellowstone, about 4 miles south of the Norris junction
    and 10 miles north of the Madison junction.
    $20 per car for a 7 day pass or National Parks Pass
  Trails:
    The wide trail is an ugly, level walk through a thin forest/
    brush with nothing interesting along the way for .5 mile.
    After that is a loop (mostly boardwalk, some dirt) through
    area that has a couple of thermal springs, some steam vents,
    and some paint pots (bubbling mud) - they are spread out a 
    little bit compared to the Fountain Paint Pot area.
  Trail Length:
    about .5 mile walk to the area and then a .5 mile loop
  Area:
    Thermal area
  When I did the hike:
    Tuesday, August 28, 2007
  Recommendation:
    Skip it - go to the Fountain Paint Pot area for 
    better thermal items.
  Fountain Paint Pot area - Yellowstone National Park
  Directions:
    In Yellowstone, about 7 miles south of the Madison junction
    and 8 miles north of the Old Faithful area.
    $20 per car for a 7 day pass or National Parks Pass
  Trails:
    A short boardwalk loop around a thermal area, including 
    several thermal springs (with their stunning blue color), 
    a couple of small geysers, and a paint pot area (bubbling 
    mud).
  Trail Length:
    about .5 mile
  Area:
    Thermal area
  Picture
  When I did the hike:
    July 2003; September 2006; Tuesday, August 28, 2007
  Recommendation:
    Absolutely.  A must to see some interesting and pretty 
    thermal characteristics in a short area.  Also do the 
    nearby Firehole Lake Drive for more neat thermal stuff
    (the one-way loop drive starts about a mile south of 
    Fountain Paint Pot area).
  Old Faithful area - Yellowstone National Park
  Directions:
    In Yellowstone, the Old Faithful area - between Madison and 
    Grant Village.  Park in the area near the Old Faithful 
    Lodge.
    $20 per car for a 7 day pass or National Parks Pass
  Trails:
    After finding out when the next Old Faithful eruption is
    (and make sure you are there for the famous eruption),
    head around on the boardwalk to the backside of the 
    geyser and take the bridge over the Firehole River and 
    walk the boardwalk loop through the thermal area that 
    includes a number of thermal springs and small geysers.
    In 2011 I decided to walk more of the boardwalk area
    than just the simple loop - glad I did as there were 
    many more neat thermal stuff, I got to see another geyser
    erupt, and just generally enjoyed myself for a couple 
    of leisurely hours (did it in the morning before the
    crowds arrived).  The boardwalk was slick at some spots
    with the water from the geysers and a cool morning.
  Trail Length:
    short to over 3 miles
  Area:
    Thermal area
  When I did the hike:
    July 2003; September 2006; Friday, August 12, 2011
  Recommendation:
    The most famous spot in Yellowstone.  Do walk the 
    area behind the geyser instead of simply being a
    tourist and only watching the geyser.  And if you
    have the time, take a longer walk in the geyser area.
  Yellowstone Falls area - Yellowstone National Park
  Directions:
    In Yellowstone, at the Canyon Village junction, head
    west into the village area and continue on the road 
    as it becomes a one-way road (early on is the right
    turn for the road to Inspiration Point) that makes a 
    half-loop mostly along the canyon's edge.  There are 
    a number of parking areas along the road.  A little 
    bit south from where the half-loop comes out on the 
    main road is a short road to a parking area for 
    the short trail to the view of the Upper Falls.  A
    little bit further south on the main road is the 
    turn for the area on the west side of the canyon.
    After crossing the bridge, the first left is to a
    large parking lot for the Uncle Tom's Trail.  The
    road continues out to Artist Point [the park 
    re-modeled Artist Point in 2007 and that area was 
    closed when I was there].
    $20 per car for a 7 day pass or National Parks Pass
  Trails:
    There are trails that going along both rims of the 
    canyon - for the east side, the trail goes from 
    Inspiration Point to the bridge; for the west side,
    the trail goes from the bridge to Artist Point - but
    most people (including me) make stops at the various 
    viewpoints and either enjoy the views from above or
    talk short trails down to better views of the Grand 
    Canyon of Yellowstone and it's two large waterfalls.  
    On the east side: Inspiration Point has a nice view of 
    the canyon.  Lookout Point (short trail down to a 
    better view) has the best view of the Lower Falls.  
    The last parking area is for a longer, switchback down 
    to the top of the Lower Falls (not that impressive).
    The Upper Falls View is a down to a viewpoint of the
    top of the Upper Falls (the Lower Falls is the prettier 
    of the two).  All the trails are packed dirt and well
    used.  They are mostly switchbacks with few steps.
    Remember, what goes down, must come up.
    On the west side: To the top left of Uncle Tom's 
    parking area is a view of the Upper Falls.  Uncle 
    Tom's Trail starts to the top right and heads through
    the trees a short bit before reaching a junction - 
    take a right.  A short bit ahead is another junction.
    Straight goes to Artist point.  A left will take you
    down, down, down.  It is not a trail, but a metal 
    staircase that has 350 steps.  But the view from the
    bottom is wonderful.  You get a good view of the Lower
    Falls from the side, a close up view of the canyon 
    walls with its orange, yellow, and green moss colors,
    and, if you're lucky, you might even get a rainbow
    in the mist.  Of course, then you have to go back up 
    all those stairs.
  Trail Length:
    Varies as too how much you want to do - short or long.
  Area:
    Two massive waterfalls, large canyon.
  Pictures
  When I did the hike:
    Tuesday, August 28, 2007; Friday, August 12, 2011
  Recommendation:
    A very pretty area.  The Lower Falls is the prettier
    of the two falls and the view from the bottom of 
    the staircase from Uncle Tom's Trail is my favorite.
  Devil's Tower 
  Directions:
    Hwy 24 to Hwy 110 and the park entrance.  Follow the road to
    the end.
    Bathrooms in the parking area
    $10 per car or National Parks Pass
  Trails:
    The Tower Trail is a 1.3 mile cracked paved loop around the 
    base of the tower.  There are a number of rock mounds near the
    trail that kids enjoy playing on.  The 3 mile Red Beds Trail
    is a little further from the tower and is a dirt trail - I
    didn't go very far on it before turning around as it wasn't
    that exciting and the views of the tower were much better 
    from the Tower Trail and I had a busy day planned.
  Trails Length
    1.3 mile Tower Trail
    3 mile Red Beds Trail
    1.5 mile Joyner Ridge Trail (not around the tower)
  Area:
    big Devil's Tower, thin woods
  When I did the hike:
    Sunday, July 31, 2005; Wednesday, July 2, 2008
  Recommendation:
    Devil's Tower is definitely worth a visit due to it being so
    unique, but it's not really a hiking destination.  Unless
    you are using equipment to climb the tower, you probably
    won't spend more than an hour or 2 here.