I was set on getting a Canon XTi because a couple of friends and my brother had them. I already had a Canon film SLR, so I was ahead of the game with lenses that would work. I did a lot of research and the D80 kept piquing my interest. Finally I went to a local shop and put those two in my hands. For me, the D80 just felt better. I also tried the D200, but my budget, which was already overextended, made me pull back. But instead of the 18-135mm, my preference was to go with the 18-55mm and a 55-200mm.
All that garble was to say, put 'em in your hand and see what fits. They all take good pictures. Beg, borrow or steal yourself a memory card for each (Nikon=SD, Canon=Compact flash) and take them for a test drive.