8. Anonymous: Ferrari 250 Testa Rossa
As one of the most expensive cars ever sold, the Ferrari 250 Testa Rossa’s owner remains a mystery. With only 21 of these cars known to be produced, one sold for $16.4 million in 2011. In 2015, it was reported a 1957 Testa Rossa sold for a whopping $39.8 million. You would have to be a billionaire in order to purchase one of these babies and still keep it a secret.