I was in the same boat and sprung for the Canon EFS 10-22mm over the Sigma due to the fact that Sigma seems to have a few quality issues,and the Canon is sharper when cropped in.
Since picking this lens I have not regretted it one bit.
Its not the fastest but with a mono pod or tri-pod it will be just fine.
Here are a few recent photos I took with it:
Keep in mind on a 1.6x crop sensor it is really like a 16mm-35.2mm compared to a full frame body.
The 10mm-22mm was designed to use on a crop body body.
Some people have switched the mount and used it on a full frame body. Not proven to be totally compatible.
If you are considering upgrading to a full frame sensor body consider the EF 16-35mm F2.8L. This will work on a crop frame as well as a full sized frame.
Just keep in mind it will not be as wide as the 10-22 on your crop sensor, however will be just as sharp if not sharper, and a faster lens.