I recently had the same choice (between the Nikon and the Canon) and went for the Canon. At the time, only the Rebel (known here as the 300D) was available. The day after I bought it, Canon announced the Rebel XT (350D). Sigh.
Like Minh says, with an SLR, the lenses are important (I'd actually say more important), and one of the factors that swayed me was the range of lenses available from Canon. Since getting the camera, I've ditched the lens that came with it (the closest thing
to cheap and nasty compared with other lenses in their range) and now have three lenses to cover my needs - two zoom lenses covering from 17mm to 200mm and a fixed 85mm lens for portrait photography.