Another vote for the Sigma 10-20 mm lens. Excellent performance and well built. Optically superb - "bent" originally straight lines photographed at the wide end can be digitally reversed by using the freeware program "ShiftN".....
Will Patterson: the Sigma 8 mm lens is a fisheye lens, not a super-wide angle lens.....it has a totally different optical design and leads to different kind of photos.