Via friends Mike and John August. Read, sign, support.
Call the Governor's office. In general, you'll reach a voice mailbox to express your support; if you get a busy signal or a full mailbox, try again later or just call a different office:
Los Angeles: 213-897-0322
San Diego: 619-525-4641
San Francisco: 415-703-2218
Sign the online petition for Equality California regarding this issue (click on "Take Action"). The petition will be delivered to Gov. Schwarzenegger next week.