Item: Leonardo da Vinci's Codex Hammer
Winning Bid: $30,802,500
As the ultimate Renaissance man, Leonardo da Vinci meticulously recorded his thoughts, musings and sketches in journals throughout his life. Of the 30 that remain, his most famous is the Codex Hammer, named for the British nobleman who acquired the 72-page journal in 1717. Three years after Bill Gates bought the historic diary, he released a digitally scanned version for all the world to enjoy.