The offical AMA/RCCA (RC Combat Assoc.) rules can be found at:

http://www.rccombat.com/asp/rules/rules.htm

These rules are what is flown at Nats and around most of the country in sanctioned contests.

You can get a lot of information on the RCCA forums at http://www.rccombat.com, it's worth a look.

The RACores Grelmin rules are used in a few places, mostly in New England. They are actually rather different from the AMA/RCCA rules