Union catalog of digital resources. This link goes to the FirstSearch advanced search interface. There is also free public access through http://oaister.worldcat.org/
The Archival Research Catalog (ARC) is the online catalog of NARA's nationwide holdings in the Washington, DC area, Regional Archives and Presidential Libraries.
Explore the rich variety of topics, images, and materials featured in online exhibitions from libraries, archives, historical societies, and museums around the world.
A listing of over 5000 websites describing holdings of manuscripts, archives, rare books, historical photographs, and other primary sources for the research scholar.
Its chief deliverable is a set of Guidelines which specify encoding methods for machine-readable texts, chiefly in the humanities, social sciences and linguistics.