Howdy,
If you shop for "Chameleons - Nature's Hidden Jewels" 2nd Ed. By Petr Necas, be sure that it is the 2nd edition since it is the more up-to-date and expanded version published in 2004. There is a companion book called "Stump-tailed Chameleons" that is often sold paired with the other one at a discount. ~$60US and paired together for ~$95 if memory serves me. I got my pair at the yearly Anaheim CA reptile show just when it came out.
"Chameleons - Their Care and Breeding" By Linda J. Davison was published in 1997 but even still, it has a lot of good info (watch out for dosing errors in the meds section). It's about 100 pages in an 8.5" x 11" glossy color format. At a retail price of $20 it makes a good intro book. I actually buy quantities of them directly from the publisher and pass them on to the local reptile store so that they have something useful to sell to their chameleon customers while still allowing them to make a little profit (none for me!).
"The Panther Chameleon: Color Variation, Natural History, Conservation and Captive Management" By Gary W. Ferguson (2004) has about 50 of its pages dedicated to images and discussion about the color variations of panthers. The other half of the book covers topics like panther history, conservation, husbandry etc. I think it was ~$35US at the show.
"Reptile Medicine and Surgery" 2nd ed. By Mader (2006) is the update to the original one from 1996. Over 1000 pages of hard-core, vet-aimed info. I refer to it often to get details on medicines, treatments etc. I'd guess that there might be 100 pages that are directly related to chameleons and another 100 pages that are indirectly related and useful to the chameleon keeper. Lots of the book is about snakes and turtles. If you have an extra ~$120US, it makes a good reference book.
"Thoughts for Food" 3rd Ed. Edited by Ardi Abate is about 50 pages of 8.5" x 11" paperback that covers about a dozen kinds of feeders and how to raise them etc. It was less than ~$20 and worth it.
"Understanding Reptile Parasites" By Roger J. Klingenberg D.V.M. is about 80 pages of 5.5" x 8.5" glossy paperback formatted black and white photos and text covering diagnosis, identification and treatment of parasites. Very handy especially if you have a nice microscope. It is usually sold for around $10.