Who is the most effective green celebrity advocate?

Leonardo DiCaprio - In 1998, he started the Leonardo DiCaprio Foundation to promote environmental causes. More recently, he's been working on 11th Hour, an environmental documentary featuring interviews with global green leaders.

Cameron Diaz - The avid surfer drives a hybrid car, got trained to give Al Gore's climate presentation, and helped make the big announcement about Live Earth.

George Clooney - Clooney launched Oil Change, a campaign to say good night and good luck to America's dependence on oil. And to drive the point home, he's frequently seen out and about with his eco-friendly Tango electric car.

Matt Damon - The talented Mr. Damon has been a good shepherd for the earth, narrating the documentary Running the Sahara and participating in the related awareness campaign about the water crisis in Africa.

Pierce Brosnan - focuses his activism on the planet -- marine mammals and wetland protection in particular. Brosnan -- who was named "Best-Dressed Environmentalist" in 2004 and serves on the board of the Environmental Media Association -- has long fought