English and Modern Languages: Digitized Primary Sources

British Library: excellent resource containing over 1,200 works, critical essays, teaching resources and more.

The LoC's digital collections include photographs, prints, A/V, newspapers, and more.

A digital library of primary sources on American social history and literature organized by the University of Michigan library. Includes a wide variety of books and magazines.

U of CA Berkeley: an extensive and ever-growing archive of original documents by and about Mark Twain (born Samuel Langhorne Clemens, 1835–1910).