
EndNote is powerful reference management software that collects, stores and organizes references for books, journal articles, and images that you've collected. EndNote helps you import references from databases, library catalogs, and websites into a document as you write it and then format your paper according to thousands of styles, including Turabian, MLA, APA, and Chicago Manual of Style.

Web-based system hosted at Catholic University Libraries to manage your source citations and to create bibliographies and citations in text. More information.
Zotero
An extension to the Firefox browser to help you collect, manage, and cite your research sources.
If you are looking for other reference management packages, check out Comparison of Reference Management software Wiki.