Finding the best fuel economy cars today is a task. Manufactures are trying to provide the best mileage possible because they know this is what the consumer wants.All you need is proper research and to compare the fuel efficiency for the best deals on the car you want.

a 3 cylinder with a manual transmission !

Probably the Geo Metro 3 cylinder motor.

Your question is a bit broad. Some might say it is the car that someone else pays the gas. Try this site since you don't specify year etc.

www.fueleconomy.gov/feg/findacar.shtml