Cambridge History of English and American Literature
Published in the early 20th century, this online version offers the text from over 11,000 pages of essays covering a wide selection of literature. Part of the Bartleby's collection online.
The John Hopkins Guide to Literary Theory & Criticism
Updated annually, this online guide "presents a comprehensive historical survey of the field's most important figures, schools, and movements." Entries and subentries are alphabetically arranged.
LIterary Criticism on textetc.com
Provides a nice overview of literary theories and literary movements.
Glossary of Literary Terms and A Handbook of Rhetorical Devices
Quick reference compiled by former professor Robert Harris.