i use Xdreme camera. It has a lot of accessories and functions but it's quite heavy to use as head cam i suppose.
For head cam i think you should be looking at smallest housing you can find (usually those round ones), maybe even with battery and memory unit separated from the camera itself and connected via a cable.
bskerj is right. First thing to do is buying extra batteries - rechargeable of course. With one battery only you will film 3-4 hours only...