I just to use the GoPro HD kit but found it cumbersome to use and mount. Since then Im running with the adrenaline systems HD 295 helmet cam kit. It has great video quality and features a super sharp TFT screen: this allows me to mount perfectly with real-time view, no to mention video preview without having to connect to a computer.

So far it has been very reliable and super light weight; I can mount and unmount on the fly without too much delay.
Check it out at:

http://adrenalinecamera.com/product_...roducts_id=342

Check out mounts for direct bike mounting which are well worth the extra bucks:

http://adrenalinecamera.com/product_...roducts_id=255