Having played with both the Nikon and Canon (from the perspective of a Canon SLR/DSLR user for a bit), I ultimately chose the Pentax K10D. The feel, the controls, the features all caught my attention, and the price was great. However, I would say that this camera has a steeper learning curve (at least for me) than Canon did.

Go to a store and play with the different cameras. Check out the review section here, and any other websites you can find (and don't forget to read user reviews). Also, check out image galleries using the models you're interested in...See what kind of images they're getting out!