I use a hatchet and chopping block to remove the head, but I first whack them in the head with a light stick of wood to stun them (something like a bare hammer handle that I can swing quickly and accurately), then I grab the head with my left hand and my wife grabs the feet and we sort of stretch the neck out for a second over the wood block, then I chop the head with the hatchet which is in my right hand. Then they go off to the scalding pot and into the motorized whizzbang chicken plucker...
I figure that whacking them in the head is instant and humane- they will either go limp or they will flop/shiver much they do when their head comes off- but just not as violently/forcefully. Once they are whacked, they are easier to manage/hold on the chopping block.
PS- Does whacking chickens make me eligible for joining the Amish mafia?