You might take a serious look at the Pentax K20D too. I think all the modern dSLRs are really excellent and it just comes down to personal preferences. You'll find plenty of praise for Canon and Nikon out there. The Pentax has IQ right on par with Canon and Nikon.
Nikon's image-reduction algorithms seem to favor detail over noise, so images sometimes have a bit more digital noise to them, but with more detail. Of course you can always apply more noise-reduction in the computer if that's your preference.
Similarly, the Pentax auto-exposure seems to refuse to blow out details (overexpose), so images can come out of the camera a bit underexposed. Plenty of headroom (Esp. if you shoot RAW) to brighten up in post.
The things I really like about the Pentax is the control system is pretty quick to use. I was a bit concerned about that at first. Canon bodies have a dedicated button for _everything_ and the Pentax doesn't, but the Pentax system is pretty quick too.
The build quality is superb. The camera feels very good in your hand and built to a high level of quality and durability.
The K20D (and K200D) are also weather sealed, so no worries about if it gets splashed or sprinkled on.
Pentax uses an in-body Shake-Reduction system, so instead of having to buy an IS-system with any lens you want to use (Canon, Nikon), any lens you slap onto the camera instantly has Shake-reduction.
Furthermore, Pentax has been using the same lens mount for the past 30 years, so you have access to a huge huge huge range of old lenses, if you're into that kind of thing.
Like I said at the beginning, the cameras all take great pictures, so I'd say pick the features and camera you like the most. If that's a Canon or Nikon, that's fine, but at least give the Pentax a look at...because I think they're great cameras and hugely underrated!