Mendeley is a desktop and web program for managing and sharing research papers, discovering research data and collaborating online. It combines Mendeley Desktop, a PDF and reference management application (available for Windows, Mac and Linux) with Mendeley Web, an online social network for researchers. Mendeley requires the user to store all basic citation data on its servers - storing copies of documents is at the user's discretion. Upon registration, Mendeley provides the user with 1 GB of free web storage space, which is upgradeable at a cost. [from Wikipedia]
Stony Brook University has a site license for EndNote, a bibliographic tool which enables users to quickly organize references while automatically building bibliographic documentation.
The library provides free EndNote workshops each semester. Check the library homepage or see the link below for upcoming dates.
Zotero is "a free, easy-to-use Firefox extension to help you collect, manage, cite, and share your research sources. It lives right where you do your work—in the web browser itself."