Medieval Music Archives and Databases
CANTUS: A Database for Gregorian Chant
Indices of chants in selected manuscripts and early printed sources of the Divine Office, at the University of Western Ontario.
Monumenta Musicae Byzantinae
The University of Copenhagen's comprehensive archive of microfilm and photographs pertaining to Byzantine chant.
Thesaurus Musciarum Latinarum
An evolving database of the entire corpus of Latin music theory written during the Middle Ages, at the University of Indiana. Browsable, searchable, and downloadable. Please read their copyright notice.