The MLA International Bibliography is the first stop for English studies. It does not contain full text for every article, but it does contain the most comprehensive list of articles and essays on literature.

The MLA Director of Periodicals contains the most comprehensive list of journals, edited books, etc. on literature.

EBSCOhost is a convenient collection of multiple databases that included citations and full-text for a variety of articles and eBooks. A note of caution: The scope of this collection is so large that you need to make sure that the sources you find are academic.

Project MUSE is a multi-disciplinary database that contains some good academic journals for literature, particularly in children's literature and American Studies.

JSTOR is a multi-disciplinary database that contains many older journals (19th and 20th c.).

Digital collection of public domain books, movies, audio files, and archived websites. Also includes older library books that are not in the public domain that can be viewed with a free membership.

Digital repository of public domain books from libraries all over the world. Most books can be viewed in whole, but cannot be downloaded in whole without a membership to an affiliated library. 

Large collection of full-text and partial-text books, magazines, etc. 

Digital collection of full-text books in the public domain. Books are transcribed by a large army of volunteers.

Digital library for ancient literature. Includes texts in their original language (ancient Greek, Latin, etc.) and English translation.

Digital collection of American historical newspapers before 1926. Supported by the Library of Congress.