Digital sheet music

General

Petrucci-library
A large digital notes-archive. Contains more than 50.000 classical titles (chamber music, symphonic works, complete operas). You can browse on composer name, composer period and work genre. The archive also contains scores from composers who are willing to share their music with the world without charge
Sibelius Music
Large database with digital scores (classical music, jazz, pop and rock)
Choral Public Domain Library
An archive with almost 9000 compositions for choir, with translations of the texts and information about the composers
Repertoire Vrouwenkoor
A digital notes-archive with music for women's choir a capella
Early Music Online
The digitized versions of more than 300 16th century music editions of the British Library.
Theaterlied
11588 Dutch songs from the collections of the Theater Instituut Nederland. Digitalized for the project Het Geheugen van Nederland.
Wikifonia
A digital notes-archive mainly for popular music and jazz (melody line, chords and lyrics)

Composers

Johann Sebastian BACH
Bach Digital (contains digital reproductions of the music manuscripts)

Ludwig van BEETHOVEN
Beethoven-Haus Bonn: digital archives (contains digital reproductions of the music manuscripts)

Johannes BRAHMS
Digitaler Notenschrank (manuscripts and scanned old editions of all opuses)

Alphons DIEPENBROCK
Manuscripts of Alphons Diepenbrock (all Diepenbrock-autographs from the collections of the Nederlands Muziek Instituut, digitalized for the project Het Geheugen van Nederland)

George Frideric HANDEL
Handel Werke (the digitized version of the series that was published by the Deutsche Handel-Gesellschaft between 1858 and 1902, ca. 100 volumes)
Händel-Haus Halle (the digitized version of music manuscripts, music editions en literature from the collections of the Händel-Haus in Halle)

Franz LISZT
Franz Liszts musikalische Werke (the digitized version of the series that was published by the Franz Liszt Society between 1907 and 1936. The 34 volumes contain the main part of Liszts oeuvre)

Felix MENDELSSOHN-BARTHOLDY
Mendelssohns Werke (the digitized version of the series that was published by Julius Rietz between 1874 and 1877 (editor: Breitkopf & Härtel)

Wolfgang Amadeus MOZART
NMA Online (the digitized version of the Neue Mozart-Ausgabe, ca. 125 volumes)
Mozart's letters (this site provides a complete, four-language, annotated searchable edition of Mozarts’ letters)

Franz SCHUBERT
Schubert-Autographe (digital reproductions of more than 500 compositions and letters in autograph)

Robert SCHUMANN
Robert Schumann's Werke (the digitized version of the series that was published by Clara Schumann and Johannes Brahms between 1879 and 1893 (editor: Breitkopf & Härtel)

Carl Maria von WEBER
Carl-Maria-von-Weber-Gesamtausgabe (digital reproductions of Von Webers letters, diaries and other sources. Not yet available in digitized format: his musical works)