I have a Canon 60D and the Canon 10-22mm. I love this lens. I have taken lots of great pictures with it. One important thing is its flare resistance. When you have a lens as wide as 10mm, the sun is frequently near your frame if not in it.
The Tokina 11-16mm f/2.8 is a better lens for indoor and low light work, but it has a lot of problems with flare when used outdoors.
The Sigma 8-16mm is the widest available UWA zoom. It is suppose to have good flare resistance, but you cannot use screw on filters.
+1. Beware of considerable chromatic aberration with the Tokina. I really love my Canon 10-22 on my 60D. Here's a shot at 10mm.