NAfME – Copyright Law: What Music Teachers Need to Know
MTNA - Copyright FAQs for Music Teachers
IMSLP - Public Domain and Copyright
Music Library Association Copyright Guide
Eastman - Sibley Music Library
New York Philharmonic - Orchestral Scores and Parts
Music Sacra - Latin and English Catholic Church Music (including chant books)
Wiki - List of Online Digital Musical Document Libraries
Digital Scores - General Collections
Digital Scores - Composer-Specific Collections
Digital Scores - Sheet Music Collections
Public Domain Opera Libretti (Stanford University)
LiederNet Archive: Texts and Translations of Song and Choral Literature
Vocal Literature - Texts and Translations (UIUC)
Library of Congress - National Jukebox
University of Michigan - Arts Research Guides
University of Michigan - Music
University of Michigan - Musical Theater
(NB - all UM-Ann Arbor online resources are available and mirrored at UM-Flint and UM-Dearborn)
Library of Congress – Digital Music Collections
Library of Congress – Music Treasures Consortium
UCLA Music Research Resources Online
Eastman School of Music, Sibley Music Library – Reference Guide
Michigan State University - Music Resources