I had a Pro Optic one:
[ame]http://www.amazon.com/Optic-Auxiliary-Super-Fish-Eye-0-25x/dp/B0002E1SQY/ref=sr_1_22/102-8774412-7587336?ie=UTF8&s=electronics&qid=1174665184&sr=1-22[/ame]
It was great fun. Had the quality of a toy camera. It didn't fit the step-up ring like it supposed to, though, so I sent it back. I've since bought a door peephole and stuck it to my point and shoot. It's the same amount of fun, equally crappy quality, and cost about five dollars.
If you're going to get a wide angle adapter, the lower the number before x, the wider it will be. Most are 0.42x, which in my opinion, is nowhere near wide enough to bother. The Pro Optic I had was 0.25x, which was great. The widest one you can get is something like 0.16x, but those are harder to find.
I recommend making a peephole fisheye adapter. It's going to have only marginally more crappy quality than a hundred-dollar wide angle adapter.