"It's a daily, sort of eternal attempt to be aware," says Adrian Grenier (Entourage). "I try to turn off the lights as much as possible; I unplug all my appliances, and I use eco-friendly light bulbs. I try to eat free-range, organic foods. I try to walk—that's why I love New York. I take the trains. My home is a green home.

"I look at it as an investment: things may cost a little bit more, but ultimately it pays for itself. Then it gives you a little profit. People invest in all sorts of bizarre things, so why not invest in your quality of life and the environment?"

What little things can you do to help the environment? Find out in our iGo Green section. Plus: Pair hot stars like Cameron Diaz and Leonardo DiCaprio to their green cause in Celebrity Matchmaker: Green & Famous.