Pi Song 

Memorize pi to 39 decimal places with this little ditty.
3.141592653589793238462643383279502884197
You could keep going with the same tune, or invent new ones...
Why would anyone want to do this? There is no really practical reason to know pi to this level of accuracy. But it's a fun bit of trivia to pull out and impress your friends. (However, if you want to break any records, you'll have to memorize it to a lot more decimal places than this. The official world record set in 2005 was 67,890 decimal places.)
Happy pi day!