Most embarassing accident - I had just picked up my new bike from the guy who used to build bikes at the club I was a member of. I was stopped at traffic lights on the way home. The lights turned green, I had both feet clipped in the pedals, and put down the power ... which all went into tightening the rear cluster and not moving me forward. I rolled forward a few metres, then gracefully tipped over ... in front of all the other traffic that had been stopped at the lights, including a couple of guys on motorbikes.

Most spectacular was probably the car that got just in front of me, then turned left cutting across my path - I went right over the back end of the car, bike still attached.

Most painful was probably the one where I was on a training ride, and started to stand on the pedals to accelerate for a sprint - my chain slipped off the outside of the front chainring, and all my force went straight down, shortly followed by the rest of me :-)
Lots of bruises in odd places from that one, and plenty of grazes ...