"Documenting the American South (DocSouth) is a digital publishing initiative that provides Internet access to texts, images, and audio files related to southern history, literature, and culture. Currently DocSouth includes ten thematic collections of books, diaries, posters, artifacts, letters, oral history interviews, and songs" (University of North Carolina).
The National Archives and Records Administration is a rich resource for U.S. history. Only a relatively small portion of the collection is available online, however. Begin on the Research page, which includes access to the [National] Archives Library Information Center (ALIC).
The Archival Facility for NARA's Mid-Atlantic Region is located in Center City Philadelphia.
"Making of America (MOA) is a digital library of primary sources in American social history primarily from the antebellum period through reconstruction. The collection is particularly strong in the subject areas of education, psychology, American history, sociology, religion, and science and technology" (University of Michigan).
Making of America Journals - Over 50,000 journal articles currently available.