Fondant is the new popular coating for wedding and celebration cakes. It's not easy to use but holds up really well for hours (unlike traditional buttercream).
Collette Peters doesn't appear to have her own website (WTF?) but her books on the subject are legendary. Also check out anything by Nicholas Lodge on the subject of gum paste. If you go to half.com, search on "gum paste flowers" or "fondant" and you'll get some great bargains on these books.
If you watched the Wedding Cake Challenge, you'll know the name Michelle Bommarito. Check out her site - although she really doesn't divulge very much on it: http://www.michellebommarito.com
For gum paste and fondant supplies: http://www.beryls.com/mainpage.htm
- when I did our wedding cake (my first foray into fondant!) I got most of my supplies from this site.