As a few have suggested, the 15-85mm is a very good lens.
It's my most used because of the range, low CA, very sharp, has great IS, fast AF and is no bulkier than the 17-55. I still have both of these lenses but the 15-85 is nearly welded to my 60D. The 17-55 comes out for some indoor shots or shallower DoF work with my older bodies.
Only complaint i have about the 18-85 is that I sometimes get severe corner shading, likely from a filter I keep on it. This is intermittent and likely a factor of the IS group being near its physical limit plus the filter not being a super-thin type. Other than that, it's provided 1000s of excellent images and lets me leave the tripod in the car a lot more.