Sounds like the Canon 17-55 f/2.8 is the way to go...would you say that it's vastly superior to the Sigma 17-50mm f/2.8 EX DC OS HSM?
Thanks for the compliment & for taking the time to check out my flickr page, KCmike!
You be the judge:
http://www.photozone.de/canon-eos/425-canon_1755_28is_50d?start=1
http://www.photozone.de/canon-eos/531-sigma1750f28os?start=1