voice4change.org: Call To Action: Register Voters at Fahrenheit 9/11:

"When voters walk out Fahrenheit 9/11 they will be ready to vote George Bush out of office. We recommend that you be waiting outside the theatre with voter registration cards. Hand them out, if someone wants 10 give them 10, people will be motivated to register their family and friends after this movie."

... especially if you (or friends or relatives) live in a "swing" state.