The Ford Probe V concept car had an amazing drag coefficient of just 0.137, which matched a penguin flying under water with its wing flippers held against the body! The squared off back end with a sharp edge at each rear corner was crucial to this low cD and is now, finally, showing up on production cars to help boost mileage figures. This was SUCH a cool looking car, including the transparent fin on top to direct air flow. This might be my favorite concept car of all.

http://www.carstyling.ru/en/car/1985_ford_probe_v/images/7051/