I’ve always had an affinity for fisheyes. Despite the vignetting and distortion, I love to get really close and still get a lot into the frame. Panorama software works well for some subjects, but it doesn’t do the same job. I started off with an adapter that screwed onto the front my stock Canon AE1 50mm lens. Now I have a Zenitar that I got cheap–but it’s a manual and I can only use it on my Nikon 6006, which means I’ve still got one foot in the 35mm world. (not that there’s anything wrong with that…)
I’ve seen people who carry around a “moon-style” hubcap, and shoot into that to get the effect.
I don’t have a real fisheye. But I have a neat-o cheap-o substitute: a “Curvatar” attachment from Spiratone. This large, heavy device screws on in front of your normal lens, and voila! you have a faux fisheye. Here is a photo that I took with my Curvatar (on a Minolta SRT-101).