During a period of just a few months, two members of the cast of Predator have opted out of U.S. Senate races. The more recent of those two is Governor Arnold Schwarzenegger, Republican of California.
According to this post on The New York Times blog The Caucus, the Gubernator has ruled out a run for the Senate in 2010. Democrat Barbara Boxer's third term ends next year.
Carly Fiorina, the ex-CEO of Hewlett-Packard, who has become increasingly political lately, with her high-profile presence in John McCain's presidential campaign, is another Republican possibility. Boxer leads in early polls, according to this Rasmussen report.