Buying an SLR camera?

I'm looking at buying an SLR camera and I've narrowed it down to 4 cameras in 2 price categories.
- The Nikon D5100 or Canon 600D (Rebel T3i) and
- The Nikon D7000 or Canon 60D

Which camera should I get for both price categories?

They're all great. Of course the more expensive ones are better but basically all dSLR's are the same.

I'm a fan of canon over Nikon to be honest. Their cameras are well built, good quality and tend to be better all around cameras. Obviously the dearer one is better but the cheaper one will still take great pictures, it'll depend on how into photography you are and how much you're willing to pay.
If you're open to other ideas I recently got the Lumix G2 and it really is an amazing starter camera, takes great pictures and videos.

(And not all DSLRs are the same)

The Rebel T3i would be your best option. However, for something around the same price, maybe you should also consider the Sony Alpha 55, which I have personally been using since the past few months and am very, very happy with it's performance.

Between d5100 and 600d it's a tough call, both are equally good, just toss the coin.
Between D7000 and 60d, d7000 is superior unless you're more into videos.

D5100 and 600D are like the most similar cameras out there right now! Articulating screen, 16 and 18MP sensor, video. I'd get the T3i.

D7000 is a bit more expensive and therefore offers much more AF points, faster AF, 6 vs 5.3fps, better build quality. I'd get the D7000.

Here's a DSLR Buying Guide - http://www.the-dslr-photographer.com/2009/11/which-dslr-to-buy/