I'm sure you'll be very satisfied with the 24-70mm L, but I (coming late to this discussion) did make the decision a year ago to get the 17-55mm f/2.8 and I've been very happy with it indeed. Although not as strongly built as an L lens, it is not flimsy either, and has served me well in my cross-country travels.


This decision was influenced by the fact that, at the time, I was only using APS-C cameras and I already had a copy of the 24-105mm f/4 L. I wanted IS for my faster zoom, and the absence of that from the 24-70mm pushed me towards the EF-S lens. It's rumored that an IS version of the 24-70mm is in the works (and this certainly makes sense from Canon's upgrade point-of-view) and when (or if) that comes out, I'll be very interested.


As of now, I believe a combination of the 7D and the EF-S 17-55 f/2.8 will leave little to be desired in terms of image quality and versatility - although you will not have the ruggedness of the L, of course.