Something around 100mm is the usual starting place: Sigma 105, Tamron 90, Canon 100. Which one depends on your budget and brand perferences; the Canon 100 non-L is about $500 cheaper then the L, but doesn't have IS. The Sigma and Tamron are both stabilized. They all have very good optics, and make fine portrait and general-purpose short telephoto lenses as well.
If you're into extreme macro (>1x magnification), the Canon MP-E is the only real choice, and it has a steep learning curve, is not stabilized, is manual focus only, and can't focus to infinity. But it opens up a whole new world if that is the world you're interested in.
Gripped 7D, gripped, full-spectrum modfied T1i (500D), SX50HS, A2E film body, Tamzooka (150-600), Tamron 90mm/2.8 VC (ver 2), Tamron 18-270 VC, Canon FD 100 f/4.0 macro, Canon 24-105 f/4L,Canon EF 200 f/2.8LII, Canon 85 f/1.8, Tamron Adaptall 2 90mmf/2.5 Macro, Tokina 11-16, Canon EX-430 flash, Vivitar DF-383 flash, Astro-Tech AT6RC and Celestron NexStar 102 GT telescopes, various other semi-crappy manual lenses and stuff.