Rokinon FE8M-C 8mm F3.5 Fisheye Lens for Canon, a set on Flickr.
i got this lens from amazon i wasn't expecting much from it since the canon lens one cost 6 times this lens but apparently i was wrong so wrong about it, it's an amazing piece of glass clean clear that gives great colors although i did work on it with photoshop a little bit just to tweak the levels but other then that its amazing. Rokinon FE8M-C 8mm F3.5 Fisheye Lens for Canon
the Canon EF 8-15mm f/4L Fisheye USM Ultra-Wide Zoom Lens for Canon EOS SLR Cameras
to be honest i didn't use it and its price make me not think to buy it, well because i'm not that serious about fisheye photography so i think this is a great alternative i highly recommend it :)