You ever watch Pride FC?? Those rules were awesome...they fought in a boxing-esque ring enclosure and the rules were a bit different. No elbows but soccer kicks were allowed. Which basically meant, if your opponent is down, you can kick him as much as you want.
Shoot, here are the differences (Thanks Wikipedia!!)
* PRIDE allows kicking and kneeing the head of a downed opponent who is on his back. This is considered a foul in the Unified Rules, which only allows kicks and knees to the head of a standing opponent.
* PRIDE allows a fighter to stomp the head of a downed opponent. This is considered a foul in the Unified Rules.
* PRIDE allows a fighter to Spike (piledriver) an opponent. This is considered a foul in the Unified Rules.
* PRIDE does not allow elbow strikes to the head of an opponent. The Unified rules allows elbows provided they are not striking directly down with the point of the elbow.
* PRIDE's matches include a ten minute first round, with two minute rest periods. The Unified rules allow rounds no longer than five minutes, with rest periods not exceeding one minute.
* PRIDE's matches are not judged on the ten point must system, rather judges score the whole fight. The Unified rules call for all matches to be judged using the ten point must system.