Having been thoroughly underwhelmed by the performance of our US Senator for California, Dianne Feinstein, I suggest there is no better protest vote than to write in
"Markos Moulitsas" on our primary ballots.
I suppose other good options might include Cindy Sheehan, who apparently did briefly toy with the idea. I'd write in myself but I'm not 30 yet.
Feinstein has done disappointing things like passing Mr. illegal-NSA-wiretap Hayden, vote for the war, spew wrongly framed hawkish rhetoric, and generally when I hear her making news in D.C. it's bad news. I don't know how much of a dent we can make in the throngs of statewide voter who will renominate her by default, but I think the more protest vote the better. Let her have some additional measure of our dissatisfaction. Maybe she'll shape up and represent us better.
Update [2006-5-31 1:7:1 by bolson]: thanks for the comment suggesting Colleen Fernald who is actually on the ballot. I like what she has to say on her web site. I think the way write-ins are counted, they actually aren't unless there's a huge number of them. So it might be better to vote for someone named on the ballot since there's a good option.