Tokina is releasing a fisheye zoom in the fall that will cover 10-17mm it's a digial-only lens so it will look fishy. I would hold off on that if you can.
On a 1.6 body, the fisheye effect might not be as "fishy" indeed but on the other hand, the ( 15mm) lens will become more "usuable".
Depending on the subject, angle and so on,result will vay from fishy till wide angle.
The Sigma 15mm 2.8 is great competition for the Canon version. equal in quality and cheaper !
The 8mm version off course is another ball game, vignetting and "fishy" for sure.
The Peleng is a nice cheap alternate, no autofocus so ya have to go manual their ( not difficult since dof is large with a fish).
Sigma will have a new 8mm coming during these days and the Tamron that Milan is refering to, seems to be a nice alternative as well.
I have a friend who owns boht the Canon and Sigma, using them mostly for underwater photography where the corner sharpness is very important. He thinks the Sigma is a better lens overall and chooses to use that most of the time. I have used both and can tell little difference--if I were to choose one, it would probably be the Sigmas based on the simple fact that it is cheaper.
