Just been thinking about buying one of the lenses mentioned in the replies, so I have read reviews on most of these in just the last week. I definitely agree that the EF-S 17-55 f/2.8 IS is something you should seriously consider, thanks for bringing this up, Matt. As Bryan alludes to in his review, it seems the only reason this lens doesn't have an "L" designation is because it is EF-S. Second to this lens, I think looking at primes would be a good idea. I am considering the 24-70 because I am anticipating upgrading to FF sometime soon, otherwise, I would think that it is not wide enough on a 1.6x sensor, but you do have the 17-40. However, the 17-55 would cover most of that range which would reduce lens change-overs. Good luck.
Stephen