WorldCat is the Online Computer Library Center’s (OCLC) online “union catalog.” It is a database of more than 1 billion records of books and other materials held in more than 10,000 academic, public, special and national libraries around the world. You can use the Advanced Search option to limit your search to “Archival Materials.”
ArchiveGrid describes primary sources for material on family and corporate histories, personal papers, and historical records with direct search access to dispersed collections and collection descriptions.
Archive Finder brings together ArchivesUSA and the cumulative index to the National Inventory of Documentary Sources in the UK and Ireland (NIDS UK/Ireland). ArchivesUSA is a current directory of over 5,500 repositories and more than 161,000 collections of primary source material across the United States.
The History Guide Contains links to a number of good websites for primary sources.
Internet History Sourcebooks Project Paul Halsall, Fordham University
Prints & Photographs Online Catalog Library of Congress
Library and Archival Exhibitions on the Web from the Smithsonian Institution Libraries with links to more than 3,000 online exhibits of library and archival materials.
Other Library/Research Guides about Primary Sources:
University of North Carolina Libraries
University of Illinois at Urbana-Champaign
BMCC Library Contains information on the distinctions between primary/secondary in sciences and humanities.