The average fuel econony for the top 3 cars is quite high. The top three are all hybrids and get fantastic gas mileage. This puts the average mpg in the low 40s for city driving and close to 50 when you get out on the highway. The Toyota Prius is the overall winner, followed closely by the Honda Civic Hybrid and the Honda Insight. These cars all combine a gas engine with an electric motor. They are all fairly small vehicles, but work just fine for around town driving and commuting. These cars range in price from about $22,000 all the way up to $35,000 for a fully loaded Prius.
For more info, see Fuel Efficient Cars: Understand the Benefits