I shoot with the Canon 20D. I went with canon because I already had a lot of Canon Glass. If you have any old EOS lenses they work with the digital bodies, you just have to factor in the digital conversion. If you have a 50mm lens it's a 1.5 conversion or a 75mm lens on a digital body.
Another thing is that there are other Canon digital bodies that aren't as expensive, but still have most all of the functions you'll ever need. Your big thing to look at is the megapixels of the "card". The higher the megapixels the better, though you will probably never need to print anything larger than what a 10 or 12 mp will print clearly.
Though it's good to get a dependable body, most of your image quality is in the lens... A great lens will elevate a mediocre body to great levels. Whereas, a great body with a mediocre lens will always be mediocre on image quality.
When you decide on a body check
ebay for people selling off their old film camera sets with all their lenses. Say someone had an old Canon EOS 35mm and they decided to upgrade and are selling their whole setup you can get some great lenses that will work on the digital canon bodies for a song! I'm not sure about Nikon's ability to interchange.
All this being said, when people ask me what to buy, depending upon their needs I almost always send them to get the D70 if they didn't already have a canon platform. Lot of camera for the money with the D70.
Good luck,
Terri