I also have the XTi, I'm a newbie photographer, so take what I say with that in mind.
I bought the canon
50mm 1.8 (cheap), which I never take off. It always takes beautiful shots. However because of the digital crop factor on the XTi, it probably would have been better to get something in the 30mm range. I'm starting to think about the
sigma 30mm. I chose primes because you just can't do better with a zoom, and they're cheaper. The majority of pictures I take are portraits, or mostly people/stuff within 20'.
I also bought a
sigma 70-200 2.8. mostly for my kids soccer/baseball games, that also is a fantastic lens.
A great website to check out different combinations of cameras and lenses is
www.pixel-peeper.com
Anyway, I really don't mind the prime zoom with your feet thing, but I think 50mm is a little too close. That 18-55 stock lens doesn't compare, I couldn't get any good pictures with it.