new Sigma fisheyes - 4.5/2.8 & 10/2.8

designed for crop sensors... looking promising:

Sigma has for the first time marketed a true fisheye optic for crop sensors, projecting a circular 180° image onto APS-C sensors. The new lens sports a focal length of 4.5mm and maximum aperture of f/2.8, HSM silent focusing and SLD low-dispersion lens elements. Aside from the 'edgy' skateboarding shots and frankly unflattering portraits often seen, circular fisheyes are actually quite useful for astrophotography and scientific applications. Pricing and availability is yet to be announced.

http://www.dpreview.com/news/0711/07111402sigma45fish.asp

The other type of fisheye lens available is the diagonal variety which squeezes a 180° angle of view into a standard rectangular format. This new 10mm F2.8 EX DC Fisheye HSM from Sigma is just such a lens. That said, it captures a true 180° vista only when mounted in front of a Nikon DX sensor - users of Canon and Sigma DSLRs make do with 167° and 154° respectively. A built-in lens hood and HSM focusing are here and the lens will focus down to 1.8cm (0.7 in) from the front surface of the lens giving a reproduction ratio of 1:3.3.

http://www.dpreview.com/news/0711/07111401sigma10fish.asp