In Hucho's very good book on car aerodynamics (unfortunately in German, let me know if I should translate any terms for you) he describes a car designed in 1938 called the Schlör-Wagen (or "Göttingen Egg") that had an amazing drag coefficient of 0.13 !
Aerodynamik des Automobils ... - Google Book Search
If you browse through the book you'll find a number of aero gems.