PDInfo.com offers a database of sheet music for songs that are in the public domain in the United States. Sound recordings are not considered public domain; however, the sheet music itself has no usage restrictions.
As of 2015, most songs written and distributed in 1922 or earlier are considered public domain. Current American copyright law dictates that a work enters public domain 70 years after the death of the author. Anonymous works enter public domain 95 years after publication or 120 years after creation.
The Public Domain Information Project allows users to search for popular and lesser-known musical works by selecting the first letter of the song's title. Click on a letter to view all public domain songs with titles beginning with that letter. For example, clicking "B" displays options such as "Baa Baa Black Sheep," "Balm in Gilead," "Battle Hymn of the Republic" and "Blow The Man Down." PDInfo.com offers high-quality reprints of the sheet music for these songs. Click the Add to Cart button beside a song listing to purchase a reprint of the song with the original copyright date.
This website also links to a YouTube.com search for each song. Click the treble clef to the left of the song name to listen to different versions of it.