Mutopia project free scores free to download, print out, perform and distribute.1770 pieces of music are now available. search by composer or instrument.
Sheet music Consortium The Sheet Music Consortium provides tools and services that promote access to and use of online sheet music collections by scholars, students, and the general public. It is fully searchable.
Harvard: Online Resources Including historical musicology, ethnomusicology, music theory, composition, and performance practice with links to archival collections, online scores and sound recordings and more.