*Tokina 10-17, Vancouver loves his. I'd stay away from 15mm fisheyes on a crop body, 15mm would be 24mm, not so fishy. I've heard great things about the sigma fisheyes in genearl, I know a lot of pro's use the 15mm sigma over the Canon (Dan Carr...), so I'm guessing the 10mm would be just as good. The 6/8mm multi-brand is good if your on a budget, but expect major CA/aberations/soft-focus/other-junk, you get what you pay for basically.
Then theres always this, lol, I wish.