Public domain sheet music.
http://imslp.org/

When knowledge becomes a part of a society, it is for the benefit of all that it is unencumbered. I believe in the free sharing and use of culturally significant information and material.

Here are some organizations and websites that promote and protect the fair use of material and information:
http://www.fsf.org/
http://en.wikipedia.org/wiki/Public_domain
http://creativecommons.org/
http://www.public-domain.org/