chap said:
Try a
Cheap Chinese Clone.
Can't vouch for the quality, but so far I've heard they are fine, I've ordered one myself.
I've got one - it works brilliantly with a very good picture quality. I haven't got anything up on youtube yet - a few things on facebook but that's secured.
You need to get a card for it - best bet is to get a class 6 micro SD card as they are fast enough to deal with the recording (otherwise they can jitter a bit).
The only pain is the mountings provided with no simple way of mounting onto a helmet. You'll need to rig up something specific from the bits supplied - I ended up with this:
https://www.cyclechat.net/
All in all, camera £15, SD card, £8, mounting £5.