I like the guys (like the above mentioned Brian Regan and Jim Gaffigan) who makes other comedians crack up. I've heard both of them on the radio with other comedians in the booth (especially on Bob and Tom) and they get the hosts and their fellow comics laughing so hard they have to pause the show to compose themselves.
You can tell when someone is just humoring another comic or just laughing to be heard, but those guys leave them gasping for air.
Same with Stephen Wright, I've heard him stop a show with one soft spoken, low key line that just brings everything to a screeching halt.
For energy, can't beat Greg Hahn. You almost have to be on meth to keep up with him.