The general consensus among Crested keepers is that the best diet for a Crested Gecko is the manufactured "Crested Gecko Diet" (also called "Meal Replacement Powder," or CGD and MRP respectively) by Repashy Superfoods. Add in some crickets or the like every now and again, and you have a perfectly balanced diet for your sticky-footed little friend. You can buy CGD directly from Repashy, or from other vendors, i.e. The Bean Farm.
There are two very good forums dedicated to Rhacodactylus geckos (including Cresteds,
Rhacodactylus ciliatus). Fresnowitte already posted one: the Pangea forum (second link in her post). The other is Repashy's gecko forum:
http://www.forums.repashy.com/. Both are great places to look for advice on Cresteds, as they're absolutely chock full of experienced gecko keepers and breeders. Much like BD.org, only for Rhacs!