Fisheye suggestion for Canon 350D

[sothoth]

I've got a 350D and would like a fisheye lens. I've never bought/researched them before. Any suggestions are helpful.

I have a 10-20mm that I really like but want to try something a little wider. It's tough to get that true fisheye effect on an camera with an APS-C sensor, it seems.

The Opteka ones seem to be of marginal quality but maybe get the job done. Looks to me like the are adapters for existing lenses, which is OK but not ideal.

Are the other options besides this and the Sigma 8mm? I'm not positive the 8mm is wide enough.

Thanks in advance.