my vote goes for the Tokina 10-17mm Fisheye, love this lens and use it loads

if you want some samples i can post them up.
It is proper fishy at 10mm and has zoom upto 17 which is nice but not really needed, its f3.5-4.6 which isn't brilliant but its good enough

i use it outside so doesn't matter, shoot at f9-11 anyway.
Other option is the 10mm Sigma f2.8 which was the 2nd fisheye I was looking at, your using a crop sensor so there are only a few fisheye that are actually fishy, the 15mm canon isn't fishy on a 1.6x crop body its wide but not as wide as 10mm.
8mm Sigma is a bit too much fish it does have black corners where as the 10mm doesn't, so you get more in then you do with the 8mm.
What do you want the fisheye for?