The best lense I can think of is the Tokina 11-16mm f 2.8 lense (the Canon mount). It has been praised as a wonderful performer in numerouse reviews and blogs for it's build quality and image quality as well as price (Much cheaper than the canon alternative).
There is a Tokina 12-24 mm f/4 canon mount also fr a even cheaper price. But the real winner is the 11-16mm version.
I'm sure you'll be a winner if you can get hold of one of these lenses