The Canon vs Nikon argument is akin to Pepsi vs Coke (hrm does that analogy work in the UK?). Both are very good, you're likely to be very happy with either. Best advice is to go play around with each at a store for a bit and see which feels better in your hand.
Between those two, the Canon has a much nicer screen on in than the Nikon does. Other than that they are pretty much identical feature wise. Are there any other lenses that you particularly want? If so, I'd compare the price of those between Canon and Nikon as well.
Personally I love my Canon 450D, and can't stand my buddies Nikon, but they both take great pictures.