There are several key elements you'll want to think of when choosing a camera for wildlife photography. Among them are build quality, whether or not you want some weather sealing, speed, and, most importantly, the lens. As Wolfsong mentioned, you'll want a lens with a long reach. It helps to have a few more megapixels thrown in there so you can crop your pictures without losing too much image quality.
There is a nice summary of things to consider in a dslr for wildlife photography in this article
from Outdoor Photographer magazine. It also lists a selection of cameras you might want to consider, but keep in mind that a whole host of new models have been released since the article was written, including the Nikon D5000, the Olympus e-620, the Canon 500D, the (announced) Canon 7D, the Pentax K-7 and (if I remember correctly) the Nikon D90. Reading through it should get you started.
The things I'd recommend over all others are speed, build quality and lens choice. You'll want a camera that is fast (i.e. starts up quickly, focuses quickly, and has a good continuous shooting rate) and can stand up to the elements, but you'll also need a lens that can zoom in- a lot. Wild animals just aren't easy to sneak up on, and unless you're in an area where a lot of habituation has taken place, you'll need to have a lens that can make it look like you're close, even when you're not.
The Canon 100-400mm L is a good choice. As Ernie mentioned, Sigma has the 150-500mm, which comes in different mounts to fit many brands: Pentax, Nikon, Canon, etc. Most brands have uber-expensive prime lenses, too, at long lengths (i.e. 300mm, 400mm, 500mm, 600mm, etc.) And the entry-level Olympus bodies have a crop factor of two, meaning any lens you mount will be, effectively, twice as long (e.g. a 100-300mm lens will become a 200-600mm lens), and Olympus glass is really nice.
Good luck, and let us know how you get on!
Nikon D300 / 35mm f1.8 / 300mm f4 / TC-14E II
Pentax K200D / DA 18-55mm / DA 55-300mm