5. Eugene, Ore.
Known as the Emerald City for its natural green beauty, this baby boomer haven and second largest city in the state has been doing the "green" thing since the 1960s. In 2008, after only one year of service, the Emerald Express, a hybrid public transit system, won a Sustainable Transport award. Cycling is the preferred mode of transportation, made possible by the 30 miles of off-street bike paths and 29 dedicated bike routes, which total a whopping 150 miles of smog-free travel throughout the metro area.