Digital Public Library of America (DPLA)
A vast archival collection of primary source documents from libraries, museums, and archives around the country. Try "Primary Source Sets" in the menu bar at the top, or "Browse by Topic."
The Library of Congress
Located in the District of Columbia, the Library of Congress is the largest repository of information in the world. Try "Digital Collections" to see examples of what LOC has to offer.
United States Holocaust Memorial Museum
Click the menu (the three bars in the upper left corner), then "Academic Research," then "Tools for Research" to find primary source documents. Try "Collections Search" or "Electronic Resources." The latter is a particularly rich collection of archival documents related to the Holocaust.
OEDb - Open Education Database
This is a collection of links to state archives, dedicated to various historical eras and topics.