Second all the comments on viewfinders.
Forget features. Unless you're a specialist photographer and have some obscure need all cameras will do the job. Useability is the most important thing by far and the newer generation of digital SLRs are at last properly useable in terms of response speed and viewfinders that allow you to see what you're taking a picture of.
Don't be tempted by old digital bodies like the Nikon D100 and forget full frame digital. Its too expensive unless you're a Pro.
Try the camera out before you commit and buy that one that is the nicest to use. You'll use it more often and take better pictures with it. Honest.
And don't get hung up on Canon versus Nikon etc. I've used both and like both. Just choose the one that feels best in use and gives you a good view through the finder.
Take it everywhere with you, take hundreds of pictures and ruthlessly delete the rubbish. Do this and whatever you buy you'll end up with lots of fantastic pictures.