The forums are a must have on the computer, but as far as a must have on the shelf, check out the book store. It has a wealth of chameleon information for books.
To me, the bible when it comes to chameleons in general (and not specific to one species) is the book "Nature's Hidden Jewel", second edition, by Petr Necas.
Then again, the bookstore of the forum has great books as well, and supporting the forum is always a good idea!
I agree with Morpheon that "Natures Hiden Jewels" is one of the best. Hard to find though. Also "Chameleons, their care and breeding" by Linda davidson is one of my favorites and "Thoughts on Food" is an excelent book published by the Chameleon Information Network that covers just about everything you would need to know about feeding. The last two I mentioned are available in the bookstore section of this forum.