Here's a gallery of fisheye shots at (I've got a self-portrait in there)--

I used to like to do street photography with it. You could walk right up to someone so that they were the largest thing in the frame, aim the lens somewhere else, and they would have no idea they were being photographed and you could get some interesting juxtapositions that way.

They can be interesting for small tunnel-like spaces, like inside a kitchen freezer or a mailbox. I believe they were originally designed for inspecting pipes.