the 17-55 is awesome. i love it, and now that i've upgraded to my 5d, it's a permanent fixture on my 40d, as my backup camera/lens combo. before the 5d, it was my star lens. if you can afford it, but it without hesitation.


i know you're looking for a general purpose lens.. but have you considered a fast prime in addition?? the 50mm f/1.4 is worth its weight in gold and won't break the bank. the 50 was my second lens, after the 18-55 that i got in the kit with my xti, and that lens changed my photographic life more than any other since. not to say there aren't a lot of great or even better lenses that i've gotten sense (my 70-200 being one of them), but the 50 taught me an immense amount about exposure and depth of field.


here's one of my "learning" pictures.. very shortly after getting my 50: