OHS Library: Art & Music: Music

Scores: free online

Arcadia Early Music Archive
CCARH Publications: scores and parts

Includes Bach, Handel, Mozart, Vivaldi. (pdfs)
Chopin Early Editions
Choral Public Domain Library
Gallica
Bibliothèque nationale de France
Harvard College Library Digital Scores Collection
Selected works of Bach family, Mozart, Verdi
IMSLP /Petrucci Music Library
Rapidly growing library of public domain scores. Over 200 composers. Browse or search
Variations Online Musical Scores
From Indiana University School of Music. Numerous composers: includes orchestral, chamber, piano, song and opera repertoire.
Beethoven-Haus Bonn Digital Archives
Music manuscripts, first editions, letters and pictures.