In the January issue of photoplus they did a test of the UWA lenses, might be worth seeing if you can still find it somewhere...
Summary from the article:
Canon 10-20 f3.5-4.5
+ Natural handling with familiar Canon layout. Crisp image quality
- Too expensive, no lens hood
85%
Sigma 10-20 f3.5 EX DC HSM
+ Reasonably fast constant aperture, usual Sigma refinements
- Optical quality doesn't warrant extra outlay
84%
Sigma 10-20 f4-5.6 EX DC HSM
+ Compact design, high quality finish, good optics
- Not the sharpest when wide open
88%
Tamron SP AF 10-24 f3.5-4.5 Di II
+ Enormous zoom range, great optics
- Autofocus a little slow & noisy compared with others
90%
Tokina AF 11-16 f2.8 AT-X 115 PRO DX
+ Stunning optics, battleship like build quality
- Lacking autofocus refinement, limited zoom range
92%
Tokina AF 12-24mm f4 AT-X 124 PRO DX II
+ Very well built with new optical coatings
- Sharpness and widest angle of view a little disappointing
79%
They covered a few fish eye lenses as well, but have left those out.
hope it helps.