The Research Library Group's centralized index for electronic finding aids and database for collection level descriptions for archives and manuscript collections.
OCLC First Search
An online bibliographic database of books, archives, manuscript collections, maps, sound recordings, musical scores, films, computer files and other materials held in thousands of academic, public, special, and national libraries around the world.
This tool contains descriptions of more than 4,700 repositories and approximately 100,000 individual collections.
National Union Catalog of Manuscript Collections (NUCMC)
This cooperative cataloging effort, operated by the Library of Congress, provides a different web interface for searching the Research Libraries Information Network (RLIN), as well as a list of other national and international archival resources.
Repositories of Primary Sources
The Special Collections and Archives staff of the University of Idaho Library maintains a linked list of websites describing collections of manuscripts, archives, and other primary source materials.
Archives Web: National Archives around the World
The Municipal Archives of Zwolle, The Netherlands provides a relatively short list of links, arranged by continent, to the national archives of many different nations.