5. Studebaker Avanti
General value today: $20,000
Why it should be more: When it first debuted a couple of years before the Mustang, the Avanti was a state of the art V8 coupe with plenty of power, disc brakes to help slow things down, and seating for four. Its polarizing design is one that not many cars have rivaled before or since -- a feat made all the more impressive by an urban legend that it was sketched on a napkin during a flight. Sadly, the car debuted during a severely trying time for Studebaker, and less than 6,000 were made before the factory closed.
In a strange twist, the Avanti lived a very long second life after new owners purchased the rights. Those subsequent Avantis, produced until 2006, were merely a shadow of the real deal, and likely aren't undervalued -- however low that value may be -- but the original is a true American classic.