Here you'll find links to a number of online sheet music collections that allow you to download and print complete works. These are generally in the public domain (copyright-free), but be sure to check the usage guidelines on each site beforehand!
Containing music from the Library of Congress collections, this resource provides biographical information about eight American choral composers (Amy Beach, Dudley Buck, George W. Chadwick, Mabel Daniels, R. Nathanial Dett, William W. Gilchrist, Margaret R. Lang, Horatio W. Parker). Details also include brief histories on specific works and links to PDF versions of the sheet music.
Part of the ChoralWiki site, CPDL is a 501(c)(3) tax-exempt organization providing free choral scores and related information (recordings, translations, etc.).
Directory of large sheet music collections accessible either through a web page or an online catalog. Many of the collections include digitized reproductions of sheet music in the public domain. Hosted by the Duke University Library.
"The Mutopia Project offers sheet music editions of classical music for free download. These are based on editions in the public domain, and include works by Bach, Beethoven, Chopin, Handel, Mozart, and many others. [...] We also host a growing number of modern editions, arrangements and new music. The respective editors, arrangers and composers have chosen to make these works freely available." May include accompanying MIDI files for some works. See the site for usage guidelines.
The Internationale Stiftung Mozarteum provides online access to the music of Wolfgang Amadeus Mozart, for the educational purposes. Please read the disclaimer on the site for information on appropriate uses for this material.
"ScorSer is the search engine for musicians, helping them to search throught hundreds of sites for scores, sheet music, tabs, backing tracks, lyrics, mp3 and other necessery information."
An archive of sheet music put together by the Eastman School of Music (University of Rochester). Searchable by keyword, with a variety of limits (voice part, arrangement, etc.).
The VARIATIONS project is a prototype project, created by Indiana University, that combines musical scores, recordings, and liner notes, for a number of works (opera, orchestral, choral, solo instrument, etc.).
