3. Boston, Mass.
It's hard to think of this city without also thinking of tea — as a commodity, not a drink. Boston ranks high among the urban green elite. Sustainability efforts include a "Green by 2015" goal to replace traditional taxi cabs with hybrid vehicles, recycle trash to power homes, use more solar panels, and use more electric motorbikes for transportation. The city's first annual Down2Earth conference was held in 2008. It's designed to educate residents about how to live the most sustainable lifestyle.