I just acquired the Rokinon 8mm f/3.5 HD Fisheye Lens with Removable Hood. It doesn’t quite give a full circular fisheye result, but it comes close on my new full frame Sony A99. Plus, it’s relatively inexpensive when compared to the Sigma. It yields some rather dramatic results and I think it will be a lot of fun to play with. The focus peaking feature of the A99 combined with the large live view screen allows for greater manual focus control.
Fisheye Fun