I was reading on Melissa Kaplan's saite, Anapsid.org, and came across a very good article she has written about supplementation. It is geared mainly towards Iguanas, but applies to all reptiles. Here's a link:
Vitamin and Mineral Supplementation for Herps
Hope it's helpful. There is lots of other GREAT info on her site, for you that are newbies to the hobby.