The 17-85, at 3 times the price of the 18-55 IS, is not worth it. Yes, it does have fast USM focusing, but it is not full frame compatible, not very sharp, and has bad distortion at 17mm. I'd suggest getting a Tamron 17-50 or Sigma 18-50 f/2.8 if you really want a step up from the kit lenses.