For travelling I would say wider is far more important than telephoto - shooting buildings, landmarks, architecture and landscapes are probably going to be your staples, unless you're going to africa or something and want to shoot some wildlife. Have a think about the new 15-85 IS from canon, otherwise I would say the 17-85 is a good choice - lightweight, decent IQ, can be had pretty cheap. Biggest benefit is having IS - screw lugging a tripod around with you when IS can be used down to like 1/4 second handheld at 17mm on the 17-85, and the 15-85 is supposed to be even better (also has better IQ, bigger aperture and costs more).