Gale Virtual Reference Library
– Over 2 dozen scholarly reference books across a variety of subjects. Brought to you by the State of Michigan via the Michigan eLibrary (http://mel.org).
Google Scholar
– Journal articles, books, and other resources across many subjects. Provides a "cited by" feature to indicate other papers containing a source paper as a reference.
JSTOR
– Complete, searchable, full text articles from over 1,000 core scholarly journals. 1878 to the most recent 1-5 years (varies by title).
Philosopher's Index
– Journals, books, and anthologies covering scholarly works in philosophy. 1940 to present.