The "best" digital camera for wildlife photography and "$800" do not belong in the same question. I'm sorry.
You are looking for "adequate for the student's budget," which will not be the best.
Unfortunately, the lens that you need will blow your budget without even getting you a camera to use it with.
I'd say that you need a minimum of 300 mm at the tele end of the zoom and 400 mm is even better to keep your body out of the animals' habitat and out of harm's way.
I'll kick myself in the morning, but you might get more bang for the buck out of Canon equipment than Nikon, even though I would choose the Nikon for myself.
Check this page for some lens ideas.
http://www.the-digital-picture.com/Canon-Lenses/Canon-Wildlife-Lens.aspx
Look at the focal lengths recommended. Read the opening thoughts. "Wildlife photography usually needs as much focal length as you can bring along or afford."
The cheapest lens on this list costs $580 at B&H. It's the 70-200 f/4.0 lens. http://www.the-digital-picture.com/Reviews/Canon-EF-70-200mm-f-4.0-L-USM-Lens-Review.aspx
If you were putting this in front of a decent 10 MP sensor, you MIGHT get by with serious photos of wildlife, as you will be able to crop somewhat without losing too much detail. This means that you'd be looking at a Rebel XTi (EOS 400D) for $675. Add a memory card and the lens for a total of $1,300.
You could do okay with an 8 MP Rebel XT (EOS 350D) for $510. The total outfit would cost $1,135.
It's not an "L" lens, but you could swap out the 70-200 for the Canon Zoom Telephoto EF 70-300mm f/4-5.6 IS Image Stabilizer USM Autofocus Lens and get "IS" plus 300 mm for $550, dropping both outfit costs by $30.
In the Nikon world, I'd look at the D40X - mostly for price. The body is $730; memory card is $45; and the Nikon Zoom Telephoto AF Zoom-Nikkor 70-300mm f/4.5-5.6G IF-ED AF-S VR Autofocus Lens for $480. This lens is on my wish list. The "VR" is for real and will help add some speed in lower light situations. The total for this outfit is $1,255, so it's about the same as the Canon 10 MP outfit I put together above. The Nikon adds a spot meter, though, which could be very helpful for long-distance metering of animals.
In fact, this last setup is my recommendation as far as bang for the buck, mostly because you get that spot meter with the NIkon.