Magic: the Gathering, EDH/Commander - Official Rules List?
The rules for Commander can be found in the Comprehensive Rulebook section 903. The comprehensive rules are officially published by Wizards here. The banlist for Commander can be found in a section of the official Banned and Restricted list. Rule 903.1 indicates that MTGCommander.net is also an official source for information about Commander, and both the banlist and a summary of the rules can be found there.