I've got the big clamp that I use for the boat - it clamps on to my bimini rail. Also, I have the head-strap for action shots. I've also got the floating mini-boom that I havent used yet.
I've seen video taken with the chest mount- it's more stable than the head mount, but appears to be a bit more of a process to get on and off.
Also, they sell a stick you can use for underwater shots, or looking back into the cockpit off of the transom.