Both MTB related... but I don't ride much road beyond commuting.

1) Riding over a ladder bridge, crossing a dry stream bed, one of the rungs on the bridge broke (which after further inspection at a later date was rotted) causing my bike to come to an immediate stop. I, however, continued forward over the handle bars catching them with my knees. So I went into the dry stream bed face-first with the bike close behind. As I hit the ground with my right shoulder, the rear end of the bike swung around and the rear tire slammed into the back of my head. I laid there for a good ten minutes trying to collect myself. I walked it out. Ended up with a mild concussion and cuts/bruises.

2) I was at the end of a long ride and powering up a trail that was cut into the side of a steep hill. I was almost at the top of this rather steep incline when my legs gave out and I realized that I wasn't going to make it. I had just started riding clipless (yeah, you know where this is going) and I tried frantically to unclip. I was like a fly on flypaper. I went over to the right and ended up rolling down the steep hill about fifteen feet with my right foot still attached to the bike. I had a huge bruise on the inside of my right thigh, all of my knuckles were bloody (how this happened I don't know), and I had a deep cut on my left arm from what I think was the chain ring. I sheepishly rode it out and drove myself to the hospital.

Good times, I miss mountain biking.