Collected Resource Sites:
IMSLP (International Music Score Library Project): Collaborative site drawing together over 70,000 public domain scores (manuscripts and editions).
CPDL (Choral Music Public Domain Library): Like IMSLP, but focusing on choral works.
Classical String Quartet: Various early sources for classical string quartet
Julliard Manuscript Collection: Manuscripts from across music history, including those by Mozart, Beethoven
Some Individual Composer Collections:
Arriaga Digital Collection: Numerous musical sources for the study of the work of Juan Crisóstomo: manuscripts scores, autographs and edited scores, etc.
Chopin Early Editions: Collected resources on early Chopin scores and editions
Digital Mozart Edition: Links to Mozart’s works through the Neue Mozart Ausgabe, digital scans of Mozart’s original correspondence, and other documents. English version available in upper right hand corner of main page.
Pleyel (Ignaz) Sources: Over 200 early printed and manuscript scores representing the work of French composer and music publisher, Ignaz Pleyel (1757-1831)
Schubert Digital Collection: Digital collection of Schubert resources, including over 500 autograph scores.
Schumann Manuscripts: Many autograph manuscripts by Robert Schumann through the Bonn University Library.