3 links
American Music Resource
amrhome.net
Searchable database of primary bibliographical and Internet sources for American music.
Digital Image Archive of Medieval Music
diamm.ac.uk
Archive of Early and Medieval music manuscripts and scores. Hundreds of scanned images available, with higher resolution ones for members.
German National Discography
lotz-verlag.de
Listing of all 78RPM recordings made in Germany from 1890-1960.