DPLA is a platform that aggregates the content of many other major collections, such as Hathi Trust, Internet Archive, NYPL, the Smithsonian, the National Archives, ARTStor, and many other large digital collections.
The UCLA Music Library's Archive of Popular American Music is a research collection covering the history of popular music in the United States from 1790 to the present. This initiative provides access to digital versions of the sheet music, and performances of the songs now in the public domain.
Music for the Nation: American Sheet Music contains more than 62,500 pieces of historical sheet music registered for copyright: more than 15,000 registered during the years 1820-1860 and more than 47,000 registered during the years 1870-1885.
An Open Archives Initiative collection of digitized sheet music from a group of libraries. Libraries include: Library of Congress, the National Library of Australia, Duke University, Indiana University, Johns Hopkins University, UCLA, and the University of Maine.