I've had three over the course of my cycling career. The first one was when I was in my teens riding near dusk. I was right-hooked by someone who obviously saw me but thought he'd try to make the right turn anyway. I ended up on the curb. A couple of scrapes, but no serious damage.

The second was a few years ago on a wet morning commute when I took a right turn too fast. The bike got sideways and then over. Kind of a surreal feeling, like it was happening in slow motion, but yet you're helpless to do anything about it. Landed on my hip/butt. Again, other than some bruising no serious damage.

The most recent one was about 1.5 years ago while riding on a side street with my wife behind the stays on the front fender came loose and lodged themselves on the side tread of my very aggressive CX tires. Once it hit the fork the front wheel seized immediately causing the dreaded end-over. Landed on my shoulder, then probably my head. Ended up with a separated shoulder and a sprained digit.

Lessons learned here:
1. Do regular equipment checks, especially in the front end--brakes, tires, fenders, etc.
2. Slow down when it's wet.
3. Assume drivers don't see you...and they're about to do something really stupid.