A standing headlock or a headlock on the ground?
There are multiple ways of getting out of a standing headlock. The 'street' guys are all going to say the same thing: "HIT 'EM IN THE GROIN".
I prefer other methods (not that I'm totally against that tactic either). Arm drag out is one, a drop sweep is another (it's some judo counter throw and I can't think of it's Japanese name). The drop sweep once done, can lead you right into an arm bar.
The ground headlocks involve, turning onto your side to assist in gaining leverage. Either hooking the hip with your uppermost leg, framing up and pushing the opponent's head away then hooking it with your leg, or bridging your opponent and rolling him over -- are all viable tactics. And, you aren't going to be able to learn them from a stinking forum. Find a teacher to show them to you (join a judo, BJJ or wrestling club).
[This message has been edited by JKogas (edited 06-16-2004).]