Gotta disagree about the Canon 10-22mm being "by far the best." The one I had disappointed me and of course it could be sample variation but for the tact that some of the reviews I've read do seem to coincide with my own experience of this lens. Of course they could have had Monday morning or Friday afternoon lenses too. The issues I had were vignetting, distortion and softness all of which can be mitigated or lived with to one extent or another but I decided that it just wasn't good enough and moved it on.
OP. There are a number of lenses in the 8/10/12-24mm type range and it might be worth looking at some reviews and trying before you buy if at all possible. Personally I replace my disappointing Canon with a Sigma 12-24mm and whilst that lens too has its critics mine performed flawlessly on my Canon 20D and later 5D.