Links which may be of interest and use.
IMSLP/Petrucci Music Library. Thousands of scores, sound files and loads of information.
Choral Public Domain Library. Many choral scores and sound files.
Cantorion. Mostly choral and song files.
Mutopia Project. "Free Sheet Music for everyone"
Musescore. Open source music editor and uploads by users.
Noteflight. On-line music editor and user uploads.
Rowy.net. about 2000 scores.
Lieder.net. Text of thousands of songs.
Art Song Central. Links to many songs, some of which can be downloaded. Also a page of further links.
Freescores. Has a choral section. Can be frustrating,
Kantorei-Noten. German site with links to mainly religious choral pieces.