Another quick thought, that hasn't been mentioned. The T3i, 60D, and 7D all use the exact same sensor. Image quality between the 3 will be very, very similar.
The differences between these camera bodies, is more to do with features, build quality and frame rates.
It has been said already, but better glass will make the biggest improvement in image quality. You can't go wrong with any of the Canon L lenses mentioned, but do not be afraid of 3rd party offerings either.
The new Tamron 24-70f2.8 and 70-200f2.8, both have gotten great reviews. The sigma 70-200f2.8 os is another one thats been good. The older Tamron 70-200f2.8 great image quality, AF is a little slow sometimes.
Just some thoughts