A continually updated list of interesting music-related digital collections from other libraries, archives, museums and organizations.
Here is a big list of digital music collections that include public domain sheet music, streaming media, manuscripts, and other historical documents. Most are freely accessible.
The Library of Congress has a large number of music-related digital collections.
The Association for Cultural Equity is a great place to explore Alan Lomax's field recordings that document historical American music traditions.
Musical Instruments by Darcy Kuronen is an iBook enhanced with forty-eight audio and video clips of expert musicians performing on rare and historical instruments, this e-book edition of MFA Highlights: Musical Instruments brings the world-renowned collection at the Museum of Fine Arts, Boston, to life.