I've had two myself. The first one happened when an idiot pulled out in front of me (on his bike) while I was going 20 miles an hour (the spedometer on my bike told me :p). My back brake didn't work at the time, so I impulsively slammed on my front brake and flipped over the front of my bike. I had a pretty nasty scrape on my elbow (it's still there! this happened two or three weeks ago) and my wrists hurt enough to keep me from writing for the rest of the day.
The second was entirely my fault, but I was the only person involved! I was riding on the day after the first snow we got (around two weeks ago, I think). It was relatively nice outside (no snow, clear skies), but it was still cold! There was an area shaded by trees where some snow must have melted and then froze to the sidewalk which I blissfully transversed. Needless to say, my wheels slid out from under me when I tried to turn and I fell. It wasn't nearly as bad as the first one, though. All I got from this one were some scraped knuckles. Plus, I don't think anyone noticed!
There was another near accident when a squirrel jumped out of these raised bushes while I was riding by them. The stupid thing came within about half a foot of my face! It scared the shit out of me.
Other than that, though, I don't think I've seen any accidents.
