The Best Digital SLR For You: Digital SLRs by the Megapixel:

Now, we all know by now, that the number of megapixels isn't the main thing about a camera. My relatively low-rated (6.1 megapixel) D70 can take shots that easily blow up to 10x15 without any visible Pixilation. That said, it's one of the many facets you can and should consider when picking up a new camera.

This guide, from digital-slr-guide.com breaks down the currently available SLRs into groups, based on their maximum image size. While not what I'd use as the prime deciding factor, it's still a damned useful resource.