InfoTrac Web
An extensive collection of critical essays on contemporary authors.

JSTOR
An online collection of more than 500 major academic research journals. Use the format ti:"xxx" (where xxx = title) to search for a particular work; au:"xxx" (where xxx = author) to search for a particular author.

ProQuest
Criticism can be retrieved by typing author, keywords for the title, or subject. Limit results to "scholarly publications"

MLA International Bibliography - EBSCOhost
Try searching using your topic plus the term critic* which will pick up any form of the word criticism.