I assume you used the search function first to see what other threads already covered this topic.
The serious answer is that the current competition in the dSLR market means that there are absolutely fabulous cameras available for a price that is so low that it needs to be considered subsidized by the manufacturers.
Not sure where you live, I'm sure there's at least some kind of big box vendor near you where you can go and hold the models. It matters more how it feels in your hand than what certain specs say. Almost no one comes to the edge of those models' performance often enough to warrant buying them based off that info alone. Again, you need to hold them, and then you need to consider the fact that you're making a system investment.
Canon and Nikon are both excellent companies that are quite serious about photography, and offer something in every price class.
Canon and Nikon are the current market leaders, but do NOT underestimate Sony, Olympus or Pentax.
Sony bought the Konica and Minolta brands, and there are some fanstastic lenses available going back 20+ years (just like the other brands.) However, Sony actually manufacturs the sensors for Nikon - so expect Nikon to have to find an alternative source for sensors. In the mean time, Sony keeps introducing new models, and they're quite good. Olympus has created a fabulous system with the E510, which also accepts Leica lenses to it's open-standard mount system. Pentax would be my recommendation, they make incredible cameras with things like weather-proofing thrown in that Canon and Nikon don't even offer at the price-points you're considering. They also have fabulous lenses going back many years, and will be around for quite a while.
So my short answer: neither, go look at Pentax.
But all of this is meaningless. What matters is that you hold the camera, and see how you feel with it.