_Bibme:  Free citation generator that anticipates sources and pulls reference content from a database of resources.

EasyBib:  Automatic bibliography and citation maker covers a large variety of source types and is updated for MLA, seventh edition.

Son of Citation Maker:  This interactive tool does MLA, APA, Chicago, and Turabian. (Just moved to seventh MLA edition too.)

OttoBib: For books only; enter the ISBN and the tool will complete the citation.