The Library of Congress classification number M1.A1 includes music printed or 'copied in manuscript' in the United States or the colonies through 1820. As an early record of musical life in America and the colonies, this classification number holds many interesting popular and topical pieces.
A virtual library of some 2,700 pieces of sheet music published in California between 1852 and 1900 and related materials. University of California, Berkeley
The Chopin collection at the University of Chicago Library includes over 400 first and early printed editions of musical compositions by Frédéric Chopin.
Began in December 1998, CPDL is one of the world's largest free sheet music sites. You can use CPDL to find scores, texts, translations, and information about composers.
Opera and musical theatre scores (G&S, Kern, Sousa, Herbert) from the University of Illinois, Urbana-Champaign. (The link takes you to the Internet Archive).
Online access to the world's most valued music manuscripts and print materials, held at the most renowned music archives, in order to further research and scholarship.
A portal to worldwide collections of medieval polyphonic music manuscripts . The music and the manuscripts date from approx 800 to 1500, and the original documents are kept in libraries and archives around the globe. Access is free to anyone, but you must register.