It used to be that the environmental movement and the business world were mortal enemies, or at least interested in different things. But that's changed. As the world's energy dilemma has become more pronounced, the environmental movement has begun to make a savvy sales pitch: Help us save the world, and we'll put money in your pocket.

We all know the outlines of the problem, of course: the energy we use to light our homes, drive our cars, and fuel our factories must come from somewhere. The best way to get it is from renewable energy sources like wind, solar, and geothermal—both to reduce our reliance on oil and other fossil fuels and to reduce the amount of greenhouse gases