If you are a US citizen and can afford it, even if you don't live in CA, please consider donating to the No on 8 campaign. There are plenty of good reasons why this amendment shouldn't pass.
Donate: Protect Gay Marriage in California
(Note that you are required by CA state law to provide your address and job title/employer's name -- if you leave them out, or put "decline to state" or something similar, they will likely have to refund your contribution.)
(If you didn't get me a birthday present this year, donate and we'll call it even. :D)