$20

Two very interesting facts about $20:

First, there's a conspiracy theory which I believe someone with way too much time made up.

Secondly, there used to be a $20 coin! Minted from 1838 to 1933, these one ounce gold coins were finally recalled in 1933 to be melted down. Now they go for about $100 on eBay. But I haven't figured out why the government melted them in the first place.