Free: Contests & Raffles.
For $600.00 I would pass on both and pick up a Canon 40D
jmx, none are great deals. You can find that Canon xsi for about 300-400 online and I have seen the lens it comes with for as low as $15. I can't comment much on the Nikon deal but it seems a tad overpriced. If you are going to spend $600, get a Canon 40D with a $50 50mm f1.8 lens... Or you can get the 18-55 canon for about $50 on craigslist.