I recently tried three lenses on my 7D (24-105, 17-40, and 17-55). I ended up ordering the 17-55 as it best suited my photographic needs (unfortunately it does not fill my red ring needs, but oh well The 24 wasn't wide enough for indoor use/some landsacpes and the 40 wasn't quite long enough for a consistent stay on my camera use. The fact that the 17-55 is not weather sealed was almost a deal breaker, however, I never feel comfortable with any of my lenses/gear getting wet in the first place.
As far as IQ, they were all excellent on the 7D. Much better than the kit lens (28-135 or 18-55)
7D, XSI, 70-200 2.8L, 100-400L, 17-55 2.8IS, 100mm 2.8 macro, 430 EX, Manfrotto tri and pod