In high-light situations, and especially in resolutions pertaining to desktop wallpapers and all online usage, the X0D line of camera from Canon are simply the best.
Don't get me wrong, Nikon and Sony are making some excellent entry-level pro-sumer cameras that anyone would love, and my decision was heavily based on legacy lenses, but Canon's outpace their direct competitors in every metric, if only by a bit.
I love my 20D. I can't say the same for Canon's later cameras, though. The same goes for Nikon and Sony. Nikon had a bit more impetus to push the envelope, since they're sort of the red-headed stepchild to Canon's Marsha, but I still feel "meh". Canon, either because they felt they could or because of technical limitations, spent the time between the 20D and what I consider its true successor, the 7D, doing nothing but raising megapixels and squeezing more ISO out of the camera.
Not like it matters! So what if the 40D can do ISO-3200. It's unusable, and at ISO-1600 it only slightly outperforms the 20D. And the per-pixel sharpness on the 20D has not yet been matched by anything less than full-frame sensors.
Now the 5D, that puppy just might have to come home.