I keep thinking I'll move into a full frame but, truth be told, it gets more doubtful as I age. For that reason I haven't spent a lot on EF-S glass but all the praise the 17-55 is getting sure impresses me.
I may break my prejudice about buying EF-S lenses and pull the trigger on the 17-55 2.8 IS when my photo-fund gets rebuilt.
I've never been an adherent of the 'I'm getting a FF camera someday so I won't but EF-S' school of thought. But the lens(es) you need for the camera you have today. Particularly if the EF-S lenses are the top ones (17-55, 15-85, 10-22), where resale value is strong. When I eventually sold my 10-22 and 17-55, I think I lost a combined total of ~$120 from what I paid new for them - pretty cheap 2-3 year rentals.
IMO, the EF-S 17-55/2.8 IS is the best general purpose zoom for APS-C. However, it is a little short for a travel lens whereas the 15-85 is better suited. If taking the 17-55, I'd be inclined to bring a longer lens, too. I found the 100L Macro IS to be a great second lens for travel, since it does both tele and macro very well, and gives you f/2.8 across the board (with the 15-85, I'd consider a 430EX II or at minimum a 270EX II).
17-55 is a great zoom if you intend to do a lot of indoor shooting, with or without flash. 15-85 would be my pick for an outdoor walk-around lens.
17-55 is also very heavy. I have one with my 7D. I also have a drebel and Tamron 17-50/2.8. This combo is much lighter, and does not lag far behind in image quality.