Ircam - Georges Pompidou Center
Institute of Research and Coordination in Acoustics - Music.
http://www.ircam.fr/index-e.html

Digital Image Archive of Medieval Music
Archive of Early and Medieval music manuscripts and scores. Hundreds of scanned images available, with higher resolution ones for members.
http://www.diamm.ac.uk/

German National Discography
Listing of all 78RPM recordings made in Germany from 1890-1960.
http://www.lotz-verlag.de/discography.html

Brazilian Music Archives
Selection of manuscripts from the Mariana Museum of Music, including rare compositions of religious music from the 17th to 20th centuries, composed mainly by lesser known Brazilian artists. Read about the pieces and view facsimiles of each page.
http://www.mmmariana.com.br/

The Keys of Atlantis
Chapter 1 of this book by Peter Wakefield Sault, that is concerned with the mathematical derivations of the western system of music, the Babylonian unit of rotation and the minute of time.
http://www.odeion.org/atlantis/

American Music Resource
Searchable database of primary bibliographical and Internet sources for American music.
http://www.amrhome.net/

Archive of Dissertation Abstracts in Music
Includes about 120 abstracts providing links to full dissertations. New submissions are welcome.
http://www.rhul.ac.uk/Music/golden-pages/Archive/Disserts/index.html

Web Resources for Research in Music
A collection of links provided by Music Department of the University College Cork.
http://www.music.ucc.ie/wrrm/

A Chronology of the Symphony 1730-1998
Lists hundreds of symphonies grouped by composer, then year by year.
http://home.earthlink.net/~kgann/Symphony.html

WWW Sites for Musicologists
Extensive collection of links.
http://www.ams-net.org/musicology_www.php

Columbia University Directory of Musicology Dissertations
Listing and abstracts for every successfully defended Columbia University musicology, music theory, ethnomusicology, and music history dissertation from 1986 to the present.
http://music.columbia.edu/dissertations/