I haven't verified this, but my wife claims there's a lens you can only buy from Canon if you buy it with a Digital Rebel which is a 180 degree wide angle lens.

She is partly right, it is the EF-S 18-55mm f/3.5-5.6 which only comes with the Digital Rebel/300D. It only fits that camera, because the rear of the lens extends back further than normal EF lenses. The DR/300D has a smaller mirror assembly than the other EOS SLRs, allowing more room for the lens to extend back. The mirror also moves differently to avoid the lens.

She is wrong about the field of view though, it isn't 180°; it is 75°-27° depending on the zoom.

It is reckoned to be a pretty good lens, given that it only costs around $120. Not nearly as good as the EF 17-40 f/4.0L though, but then that costs six times as much.

Oddly in the Japanese market the lens has proper USM focusing, but not in the US or Europe.

http://www.usa.canon.com/eflenses/lenses/ef_s18-55_35/ef_s18-55_35.html

Some people have sucessfully trimmed down the rear of the EF-S 18-55mm to make it fit normal EOS SLRs.