sigma 10-20 is quite a popular wide angle lens. the lens is good enough for me and few other pentaxian who owns it. u can google for reviews before deciding to buy or not.
Some of the pros i can name u is the the "wideness" of having 10mm, and a relatively good price as compared to other wide angles.
The photo do get a little soft at the side, but this is really not an issue with photoshop.