After being completely disappointed with the autofocus performance (or lack thereof) of the Tokina 11-16mm f/2.8, I purchased a refurbished Canon 10-22mm f/3.5-4.5 to replace it. So far, I'm really enjoying the way the world looks through this lens.
Canon 50D, 10-22mm f/3.5-4.5, f/3.5, 10mm, 1/125 sec, ISO 200
strobist: 1 Vivitar 285HV, camera left, 1/16 power, 1/4 CTO gelled and fired through a white umbrella. Triggered via Cybersyncs. You can see the full-sized images on flickr (just click on the images).