My SLR system is Nikon, but I have shot on a variety of Nikons and Canons. Both are terrific makes of camera, and you won't go wrong with either brand.
Choose the system that feels right for you. Make sure you play a bit with the cameras in real life before you purchase them. If you go the SLR route and start buying lenses for that system, it becomes a long-term relationship with that brand, so make it something that you really like.
Bear in mind though, that although SLR cameras will provide superior quality and better performance in general, and although interchangeable lenses allow for flexibility, all of these features come at a rather substantial price. If you're shooting chameleons and other small animals, at some point you'll have a need for macro capability (the ability to focus on an object from a close distance and/or to achieve good magnification of a subject), and a macro lens is another specialist lens you'll have to buy. If you want to shoot wildlife in the bush, you'll need a telephoto lens, and prices of good quality telephoto lenses useful for wildlife shooting start at more than double the cost of an entry-level SLR body...
So if you're still starting out in digital photography, and you want to keep to a budget, but still retain features, keep some of the high-end digital compact cameras in mind. For example the Canon Powershot G7, or the Canon Powershot S5 IS: both have decent wide and telephoto capabilities, and have built-in Image Stabilisation (which costs a lot extra in the interchangeable lenses for SLR's). They won't match the performance of most SLR's, but they usually contain a lot more built-in features. That can provide you with the flexibility you need when you're starting out in photography.
Go to
http://www.steves-digicams.com/ and
http://www.dpreview.com/, and read plenty reviews. That will give you a better idea of the features that are good-to-have, nice-to-have, and must-have. And then go out and play with some cameras at photography stores. You must enjoy how it feels and operates.
Also, if you're starting out in digital photography, check out this site:
http://www.dpchallenge.com
It's got a great community of photographers (much like these forums have for chameleon-lovers), and you can learn a lot there; not just about actual photography, but also about post-processing, which is a vital element of digital photography (well, even film photography, but that doesn't involve Photoshop...).
Good luck with your decision. Looking forward to seeing your pics when you get shooting...
