Mendeley is a free citation manager available from http://mendeley.com. Please note that you do not need to choose an institutional login; the software is free and Virginia Tech does not have an institutional license. It exists in both a desktop version and an online version. What makes Mendeley unique is that it's also a social network for academics. In addition, Mendeley suggests new citations to you based on what's in your library already. It also allows you the chance to share your library with others as well as annotate PDFs.
Adding references to Mendeley
How to use the MS Word plug in to add citations from Mendeley