Chazzanut Online - Jewish liturgical music site, with a large collection of cantorial sheet music, midi, links and background information.
Henry Purcell - History and some scanned manuscripts.
Historic American Sheet Music - The Historic American Sheet Music Project provides access to digital images of 3042 pieces of sheet music published in America between 1850 and 1920.
Music for the Nation: American Sheet Music, 1870-1885 - From the U.S. Library of Congress. Tens of thousands of songs and instrumental pieces registered for copyright in the post-Civil War era. Digitized images and some audio clips.
Sheet Music from Canada's Past - Features Canadian sheet music from the First World War era and from the pre-confederation era, from the National Library of Canada.