I'm in the market for an ultra-wide angle lens for my 30D. Right now my primary lens is a 28-135 IS which is quite good. I primarily shoot winter sports (skiing, snowboarding) but also do summer sports (dirtbiking, hiking, mountain biking, etc) and landscapes/nature. I'd like to get something really wide for those dramatic blue skies in the mountains. Right now I've been looking at the Canon EF-S 10-22 f/3.5-4.5 USM and Sigma 12-24 f/4.5-5.6 EX DG HSM. I'm open to other suggestions. I've also thought about getting a fisheye but I'm going to wait on one of those.
Pros for the Canon:
Excellent reviews. Not much for distortion, excellent sharpness, faster maximum aperature than the Sigma.
Doesn't work with full-frame cameras (I do plan on adding a full frame camera to my arsenal down the road).
Pros for Sigma:
Works on all cameras. Cheaper than the canon.
Sigma seems to have quality control issues so some lenses are very good, others have sharpness issues. 2/3 of a stop slower than the Canon throughout the zoom range.
As stated above, I plan on buying a full frame camera, but probably not for a year or more. Also, since I primarily shoot ski/snowboard photos the maximum aperature issue isn't much of an issue at all since I normally shoot at f/8-22.
Any other lenses I should think about?