Take a look at the "what's in your bag" thread... you will get an idea of what most are using on their 30/40/50d's, which are the same 1.6x crop as the 7d.
After reading about every photography thread on here... The lenses you will hear the most about are:
- Canon 24-70mm f/2.8L or the Canon 24-105mm f/4L for general purpose
- Canon 70-200mm f/4L or Canon 70-200mm f/2.8L as a good telephoto lens.
One lens that not many on here have, but I just bought and love, is the Canon 17-55 f/2.8 IS lens. It's expensive for non-L build, but image quality is very, very good, and it covers a nice range on a crop body camera. I went with the 17-55mm f/2.8 because I have found that there are times when 24mm is not wide enough, and having fast glass at f/2.8, combined with IS, was very attractive to me because 99% of my photos are handheld -- and I wanted a lense that would perform well indoors with low light.
(Message edited by phenom_1819 on October 06, 2009)