Here are some of the resources around the web I've used for my research.
Medline front end from the National Institutes of Health web site.
Johns Hopkins University Search Engine
The Merck Manual of Diagnosis and Therapy
Vitamin/Mineral Information from WebMD
ThriveOnline Vitamin and Mineral Guide
Supplement Watch Reviews and information about supplements
VitaminsPlus A nice reference!
Solgar Quick Guide to Vitamins and Minerals If you want quick information, here's where to go.
Ask Yahoo This reference wasn't informative on vitamins at all, but I found the "Next question" on the left side of the page quite interesting. (The question was, "what is the meaning of life!")
And with that, I'll close. Stay healthy!