Zotero (pronounced "zoh-TAIR-oh") is a Firefox addon that collects, manages, and cites research sources. It's easy to use, lives in your web browser where you do your work, and best of all it's free.
Zotero allows you to attach PDFs, notes and images to your citations, organize them into collections for different projects, and create bibliographies.
It automatically updates itself periodically to work with new online sources and new bibliographic styles.
"Zotero collects all your research in a single, searchable interface. You can add PDFs, images, audio and video files, snapshots of web pages, and really anything else. Zotero automatically indexes the full-text content of your library, enabling you to find exactly what you're looking for with just a few keystrokes."
There is a Grace Research Guide available to help you use Zotero. http://libguides.grace.edu/zotero