For crop sensors like yours (and mine, XSi) the EF-S 17-55mm f/2.8 IS is highly regarded.
http://www.amazon.com/Canon-EF-S-17-...8913512&sr=8-1
It has some of the same glass elements in an L lens, but Canon won't put an "L" label on the EF-S line. It's a huge improvement over the 18-55mm kit lens.