you can always look at the 11-16 f2.8 tokina which is supposed to be pretty goodpersonally i think the 24-105 f4L + canon 10-22 EF-S lens make a pretty nice combo
not that the 17-55 is bad or anything but the 24-105 is a really nice versitle lens and the 10-22 is pretty good for when you need to go really wide
Dido. I came very close going this route when I sold my 15-85. But because one of the reasons I decided to sell it was for a weather sealing, I went with the 16-35 and 24-105. I'll have to hold off on ultra wide shooting until I get a FF body.