The duo appear in a series of PSAs for Act Green, an effort to unite to conserve energy and reduce reliance on oil. While Paltrow uses chlorine-free diapers on her children, Diaz recycles, buys recycled goods and has gone so far as to admit not flushing the toilet every time she goes. (Hmm ... too much information?)

Portman, a vegetarian and animal rights advocate since childhood, doesn't eat or wear animal products -- not even on photo shoots. For Spring 2008, she has her own line of vegan footwear with T� Casan. And she acts as Ambassador of Hope for the Foundation for International Community Assistance (FINCA) Village Banking Campaign to bring financial services to the world's lowest-income families.

Blanchett, who helped launch the Australian Conservation Foundation's Who On Earth Cares campaign to reduce greenhouse pollution and avoid dangerous climate change, filmed a special appeal for SolarAid that was screened at the Hay Festival of Literature and Arts in Wales. The fan of eco-friendly jeans by Edun has also taken steps to reduce her carbon emissions by converting her Sydney home to a green one, timing her showers (and using a water-efficient shower head), and driving and flying less. (She has been seen riding eco taxis and buses.)

A supporter of sustainable, fair-trade clothing, Miller owns a carbon-neutral clothing line, Twenty8Twelve. The Environmental Media Association (EMA) Futures Award winner also promotes and raises awareness of carbon emissions as an ambassador for UK-based Global Cool, a campaign to address global warming.

The "Heroes" star and campaign spokesperson for Save the Whales Again made headlines when she protested with a group of surfers to stop local fisherman from killing pilot whales in southwestern Japan. Her efforts garnered her the Wyler Prize at the 2008 Genesis Awards by the Humane Society of the United States (as well as an arrest warrant in Japan). She also supports the World Wildlife Fund (WWF), a global conservation organization.