If you put your foot in it, be sure it's your best foot.
--Mae West
Calling Ideas for May 15, 2012

This is:

L. Frank Baum's Birthday
Baum wrote The Wizard of Oz (and a bunch of other Oz books).

A good day to break out "Over the Rainbow". I also found a disco medley of songs from the movie on an album with some other disco medleys that might be fun, so I ordered it from Amazon: The Best of Meco.
A&M Records released Close to You by the Carpenters
A&M Records released Close to You, the Carpenters second album. The title song became the first of six consecutive million sellers by Karen & Richard and led to a Best New Artist Grammy for the duo

Shakedown has a singing call version of Close To You (available as an MP3 only).
Relive Your Past By Listening to the First Music You Ever Bought, No Matter What It Was!, No Excuses Now Day
How about doing the first singing call that you ever performed in public? Or the first square dance music you ever bought?
English discover and name Cape Cod
Bartholomew Gosnold, an English explorer, visited the Cape in 1602 and named it for the abundant fish found in surrounding waters.

Good day for using the singing call "Old Cape Cod". The song was originally done by Patti Page, and redone by Bette Midler (and probably many others).
First machine gun patented
The Puckle gun was a British flintlock machinegun invented by James Puckle in 1718. It took a nine-round revolving block, was mounted on a tripod and was designed to be portable and especially to prevent an enemy boarding a ship. An unusual feature was that it fired square bullets.

Good day to workshop Crossfire.