All of these sources are available for free and do not require a login.
Please let me know if any of the links do not work.
- Neue Mozart-Ausgabe (Mozart's complete musical scores available as PDF files)
- Sibley Music Library scores (scores and manuscripts available for download)
- Mozart Ways (annotated letters and historical information in multiple languages)
- Digital Archives of the Beethoven-Haus Bonn (sketches and manuscripts)
- Schumann-Autographen (digitized Schumann manuscripts)
- New York Philharmonic digital archive (programs, manuscripts, etc from the orchestra)
- Music Treasures Consortium (manuscripts from the Library of Congress, Harvard, and more)
- IMSLP (wiki of public domain sheet music available for download)
- Choral Public Domain Library (choral-specific sheet music available for download)
- Gramophone Archive (free online archive of the venerable British magazine)
- Opera Liber libretti (public domain libretti searchable by librettist; site is in Italian only)
- Juilliard Manuscript Collection (digital collection of 130+ manuscripts)
- Great Conversations in Music (short films with musicians produced by the Library of Congress)
- Met Opera Archive (history, photos, and multimedia related to the New York opera house)