During Saturday night's Dan Miller-Demian Maia fight at UFC 109, Joe Rogan mentioned that Miller had a "killer guillotine" in his days in the International Fight League, and that you can watch the video online. Here's that video from YouTube.
That choke came during a fight between Miller and Dave Phillips in 2007. Miller clamped on what IFL announcer Bas Rutten called the tightest guillotine choke he had ever seen, and Phillips, who didn't tap out in time, was choked unconscious before the referee stopped the fight.
It was, as Rogan said, the ugliest, nastiest guillotine you'll ever see.