I bought an Activeon CX Gold to use as a helmet cam on my motorcycle. Mainly to be used like a dash cam in case I get into an accident and cannot speak for myself. I got it for around $40 from Target about two years ago. I've been thinking about mounting it to the bicycle for the same purpose on my commute. Anyway I think the picture quality is quite acceptable.
Here is a rather boring video of one of my weekend rides on the motorcycle. Just to give you an idea of the video quality.