19th Century American Literary, Historical, and Cultural Studies - Sponsored by the American Studies program of Washington State University, this site has an extensive collection of primary sources from the late 18th century to early 20th on topics ranging from prominent individuals to African-American women and Native Americans.
The American Memory Project - From the Library of Congress. Topics include folklore, culture, African American history, government, immigration, war, Native American history, women's history and more.
Avalon Project - From Yale University. Documents in Law, History and Diplomacy.
EuroDocs provides links to key Western European historical documents, which are either transcribed, reproduced, in facsimile or translated. Most of these documents are not easily accessible from any other source.
Government Information - Links to numerous 19th and 20th century government publications in areas of Census, foreign policy, law, legislation and more.
Historical Census Browser - Geostat Center: Collections from the University of Virginia Library - Census data from 1790-1960.
Repositories of Primary Sources - "A listing of over 5000 websites describing holdings of manuscripts, archives, rare books, historical photographs, and other primary sources for the research scholar."
dmoz Open Directory Project - an eclectic compilation of resources, including access to some source documents. History related topics are found under Arts > Humanities > History. "The Open Directory Project is the largest, most comprehensive human-edited directory of the Web. It is constructed and maintained by a vast, global community of volunteer editors."
NetsSURF - Provides access to medieval documents, authors and more.
Indian Affairs: Laws and Treaties - "Indian Affairs: Laws and Treaties, compiled and edited by Charles J. Kappler, is an historically significant, seven volume compilation of U.S. treaties, laws and executive orders pertaining to Native American Indian tribes. The volumes cover U.S. Government treaties with Native Americans from 1778-1883 (Volume II) and U.S. laws and executive orders concerning Native Americans from 1871-1970 (Volumes I, II-VII). The work was first published in 1903-04 by the U.S. Government Printing Office."