[fiskebent]

I'm a Canon guy - 1D Mark II.

There's not a lot of difference between Canon and Nikon anymore, but I like that Canon seem to think full-size sensors is the way to go with DSLRs. I also think having the focusing engine in the lenses is an advantage and since Canon have been doing it that way for a long time, their lens catalog is a bit more uniform than Nikons, imo.

Canon also have some specialized lenses that I don't think Nikon can match. Like the 50 mm f/1.2, 85 mm f/1.2 (which I have) and 200 mm f/2. And tilt and shift lenses. Somebody correct me if Nikon have lenses that match these.
They're expensive though, so it doesn't matter too much to the average photographer.

I have a couple of friends that own Nikons and they're all happy with their cameras. You really can't go wrong with either brand.