The Sigma 8-16mm F4.5-5.6 DS HSM ($1,100 list) is a lens that either speaks directly to your soul or you find nearly impossible to use effectively. It's available for Sigma, Canon, Nikon, Sony/Minolta, and Pentax APS-C cameras , where it produces a field of view equivalent to 12-24mm in classic 35mm...
Very, very wide; One-of-a-kind lens
Extreme distortion on the wide end; Relatively slow aperture; Softer at wide angles