Not all eco-celebrities are annoying. Even when she's on YouTube telling us to turn down our thermostats "just, you know, one degree," Sienna Miller, 26, manages a self-awareness that charms where other high-profile green prodders aggravate. Miller has hit on a simple rule that's eluded older socially conscious celebrities like Susan Sarandon and Ted Danson: Put down the megaphone. Instead, the actress, whose breakthrough role was in 2007's Factory Girl, has chosen subtlety. In 2003, she turned out in sustainable clothes from People Tree, telling Britain's You magazine, "There's no reason why organic and fair-trade clothing can't be sexy." More recently, she's lent her face to Global Cool, Orlando Bloom's project to cut global CO2 emissions by ten billion tons. Miller's since become an icon of the movement, this year winning an EMA Futures Award from the Los Angelesbased Environmental Media Association. She recently launched the women's fashion line Twenty8Twelve with her sister, Savannah, and has four feature films in production. With that schedule, Miller doesn't have time to be shrill.