Music Scores / Sheet Music

International Music Score Library Project with over 102,000 works that have scores or parts on Petrucci Music Library.

Choral Public Domain Library. Here you will find free choral/vocal scores, texts, translations, and other useful information.
HymnWiki is a site dedicated to hymns, children's songs (those associated with churches and religion), religious anthems, church music, other music commonly grouped with hymns, and compilations of such.
Art Song Central is principally an archive and directory of free, printable sheet music for singers and voice teachers. An emphasis is placed on standard classical and traditional repertoire.

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.
Open Music Library brings together music scores from the world’s digital collections as well as peer-reviewed journal articles and books. Currently in Beta.