SSU students, faculty, and staff have access to EndNote Web! Collect and organize your references with EndNote Web and use the Cite-While-You-Write for Microsoft Word plug-in to have your citations formatted in APA, MLA, or any other styles.
Free reference manager. Automatically generate bibliographies; import and annotate PDFs; collaborate easily, find relevant papers based on what you’re reading, access your papers from anywhere online; iPhone app
A chart from Mendeley's website, comparing citation tool features. It's from Mendaly so there may be some bias (it tends to highlight functions that Mendeley has, and leave off functions that others also have!), but it's a pretty good chart.
FREE plug-in for Firefox that allows you to store and organize citations as you find them. Also allows you to "drag and drop" citations to create your bibliography. Create groups, add a wide variety of items, store a snapshot of a website. Offers 20+ styles.