American Musicological Society
https://www.amsmusicology.org/
The American Musicological Society's purpose is to advance scholarship in the various fields of music through research, learning, and teaching. To do this, it publishes a Journal and a blog, holds an Annual Meeting, supports books in musicology, and offers a broad array of grants, fellowships, and awards throughout the year.
Early Music Online [Royal Holloway, University of London, and British Library]
http://www.earlymusiconline.org/
Early Music Online is a new internet resource consisting of digitised copies of early printed music. The project has currently digitized more than 300 of the world’s earliest surviving volumes of printed music, from copies at the British Library. The digitized music is freely available to all online.
IMSLP/Petrucci Music Library [Brigham Young University Library]
http://www.imslp.org/
The International Music Score Library Project is a wiki site that contains over 340,000 public domain music scores. Users can create accounts and upload their own scores as well.
Jazz Archive [Hamilton University]
http://www.hamilton.edu/jazzarchive/
A collection of over 300 interviews with jazz artists and other influential figures of the big band/swing era. Full text of transcripts and audio tracks are available. In addition to the interviews, brief biographies, and samples of the individual's music are also available. Only a handfull of interviews are available for online viewing, but the rest are available on DVD via Interlibrary Loan. (as reviewed in Choice, Feb. 2013)
Juliard Performance Recordings
http://jmedia.juilliard.edu/digital/collection/p16995coll3
Discover, listen, watch, and explore recordings from past Juilliard events. The collection contains most recordings of Juilliard performances from 2012 to the present, as well as selections from prior years dating back as far as 1951. Video recordings are also available of selected Dance, Drama, Opera, and Jazz performances. Recordings of new performances are added as they become available, and retrospective recordings are being added on an ongoing basis.
MusRef [Brigham Young University Library]
http://lib.byu.edu/sites/musref/
This excellent resource contains an online bibliography of music and dance bibliographies and reference sources (both print and online),a blog devoted to music and dance bibliography and reference, Basic introductions to reference tools intended to help students understand how reference sources can guide them to appropriate research materials, Links to unpublished bibliographies, and a corresponding Facebook page designed as a forum for interested librarians, scholars, and students.
New York Public Library for the Performing Arts
http://www.nypl.org/locations/lpa
NYPL's Performing Arts Library at Lincoln Center offers both circulating and research collections, including many primary sources. They also offer exhibitions, public programs, and research services.
Rare Music Materials at Stanford
https://exhibits.stanford.edu/rare-music
This site presents rare music materials from the Stanford University Libraries' collections that have been digitized in response to research requests, or were produced for small projects. At present, only a fraction of Stanford's rare music holdings are available in digital form.