WARNING: Whatever you do, please do not put the IPF in potential legal hot water by singing the Happy Birthday Song.
The 'Happy Birthday Song' is copyright protected and the owners of the song receive about two million per year in royalties. The song is currently owned by the Sammy-Burchard Company, a part of the giant AOL conglomerate. The revenue is split between AOL and the Hill Sisters.
Here is an interesting look at the song's history:
snopes.com: Happy Birthday Copyright