This is the one that everyone hunts for.... Ultra wide for crop bodies in a constant f/2.8 aperture is not easy to find. Actually, this is probably the only one on the market at this point in time. This lens is highly requested also because of its high quality optics and it's price point.

The Tokina 11-16mm f/2.8 AT-X 116 Pro DX Lens is an ultra wide angle, short zoom range lens specifically designed for use with digital SLR cameras. The slightly shorter zoom range of this lens over the popular and award winning 12-24mm lens makes it possible to maintain optical quality even at wide-open apertures. This lens features a fast constant aperture of f/2.8, and provides a focal length equivalent to 17-25mm in 35mm format.