It all comes down to how you intend to use the camera, and how much you're willing to shell out for that usage. There are tons of people who don't care about switching lenses at all -- that is why general purpose walkaround lenses such as 15-85, 17-85, 18-135, and 18-200 are made (and more importantly, why they are so popular). At the same time, not everyone care about absolute image quality. If they do, the only lenses Canon would see are 17-55 F/2.8 IS and the various L-lenses.
Realistically and specifically, how much is the OP looking to spend? If purchased locally, even the 18-135 is a ~$600+tax lens. The 18-200 is ~$750+tax, and the 15-85 is ~$1000. They are cheaper if you buy from the States (BH Photo is a good place), but at the end of the day, lenses are NOT cheap.
Also, how many lenses and how much gear do you want to bring when you head out? If you intend to haul your LowePro backpack with full gear every single time you shoot, more power to you and I admire your dedication. The majority of casual photographers that I know, however, only wants to carry the minimal amount of stuff.
-Lik |