If you want to go really wide with your APS-C sensor digital SLR, the Tokina AT-X 116 PRO DX 11-16mm f/2.8 wide-angle zoom lens offers what may be the best performance and optics available. You pretty much get it all with this lens. And I want one.

Tokina AT-X 116 PRO DX 11-16mm f/2.8 Zoom Lens Announcement
All 2009 PMA Tradeshow Coverage