Mental_Floss has a round of up of interesting US currency — including some interesting tid bits about the largest bill ever printed — the Series1934 $100,000 gold certificate.
The Bureau of Engraving and Printing only made these notes during a three-week stretch during December 1934 and January 1935. Even the few plutocrats who had that much cash during the Depression couldn’t carry one of the $100K bills, though. They were only used for official transactions between Federal Reserve Banks, and the Treasurer of the United States only issued them to Fed banks that had an equal amount of gold in the Treasury. The note featured a picture of Woodrow Wilson.
They also go through the rest of the odd currency denominations. I’ve only ever seen the $2 and the $500. I knew someone who used to keep a $500 bill in his wallet for luck. It seemed to work.