Canon EF-S 10-22mm 3.5–4.5 USM
Canon´s super-wide-angle lens for crop-sensors only. A great lens! Though it´s very tempting to use it frequently, I try not to overdo with it. Considering that only a few pictures per gallery should be super-wide, I tried the significantly cheaper Sigma-pendant but was very disappointed with it´s heavy flare. Not even good enough for just a few shots, so I got back to good ol´ Canon and didn´t regret.
Recently I had the chance to compare this lens with the no-compromise-super-wide-angle Tokina AT-X Pro 11-16mm 2.8 DX II
While there was no difference in image quality, the Tokina did have horrible focusing issues. Totally useless for me, hence another convincing experience pro Canon.