We bumped this back up to the top with new information...
Los Angeles - go to the LA Vote Site for the form (PDF format). You can fill it out onscreen, then print it out for submission - all the instructions are there.
The rest of California should go here.
Other states - simple. Do a Google seach for "absentee voting (your state)".
Our overseas correspondent, Kevin, points our nose in the direction of the Overseas Absentee Voting site if you live out of the country.
If you have a friend or family member serving with the military overseas, see the Federal Voting Assistance Program.
Do this now. Don't let this slide.