HELP, in search of a quality wideangle

[©AnderGraph]

i need something good for landscapes and shooting still life (inside a lightbox)

any recommendations, it needs to be pretty wide (due to my 20D having a 1.6 crop factor)

im looking at the 17-40L and had a quick glimpse at the 12-24 sigma.

i briefly looked at the 16-35 (which i want) but then looked at the price, which is twice as much as the 17-40 (or at least is here in the uk). im open to non canon lenses as long as they are really good quality.

any sample shots are appreciated