Hi Mitch, I haven't used the 18-200 so I can't say anything good or bad about it. Canon probably will not come out with a lens that renders it obsolete for a while though. However, if you are happy with the 17-85, why not keep it? Then, to get the extra reach check out the 70-300 IS. They would complement each other perfectly. With the two lenses you could go from 17-300mm, 17-85 for closer work, 70-300 for the reach. The 24-105L is an excellent lens as others have also mentioned, just a little pricey compared to the 17-85 or 70-300. Just some more options to consider, hope it helps.