2010 Toyota Prius

Take your cues from the interactive energy-data screens, which tell you how to drive more efficiently, and 55 to 60 mpg in the 2010 Prius is within reach. On this third-generation model, a more-efficient gas engine, better aerodynamics, and a host of other small improvements—for example, this Prius is the world’s first car whose air conditioner is driven entirely by battery—add up to 10 percent better fuel efficiency than the previous iteration. And you can expect the Prius to get even more efficient in the future: This fall, Toyota began testing a plug-in model that can travel up to 12 miles on electricity alone before switching to gas-electric operation.
From $21,000; toyota.com