I wouldn't necessarily leave Canon out of the picture entirely, as 30Ds and 40Ds can go anywhere from $400-$700, leaving you plenty of room for a solid lens still.
I do agree that the investment will be in the lenses, and recognize you are buying into an entire system (bodies, lenses, flash system, etc). Ergonomics are part of what can separate the Canon and Nikon crowds, so I'd recommend you go into a local camera shop, and handle some of the various cameras. Both brands can produce fantastic images, but one might suit your hands and preferences more than the other.