Mendeley is one of the citation tools supported by the library. It's strengths are PDF management--it can automatically import citation info from publisher PDFs and provides a built in PDF reader and annotation tool--and the social network built on top of the citation database and storage network created by it's users. On the network you can create a profile, including your own publications, participate in public and private groups, follow colleagues, and search for both papers and people. The citation tool is robust, with hundreds of styles from the standard APA and MLA to journal specific standards. There is even a citation style editor for customizing styles if the one you need isn't available. Mendeley has online storage, or you can coordinate with a desktop/cloud storage option like Dropbox. Mendeley's networking and organizing features can be used exclusively online, but the citation features need the desktop software (which can be used exclusive offline as well.)
Note: Mendeley is owned by the publisher Elsevier (producer of ScienceDirect).
The Library's guide to Mendeley:
The Zotero Citation Manager excels at importing information from a wide variety of sources. With the web browser importer installed, you can import not just individual records but entire results lists, plus associated PDFs, webpage snippets, and links. It's by far the best option for use with Google Scholar, library catalogs, and other resources that have no or limited export options. You can use Zotero's online storage, coordinate with a desktop/cloud storage system like Dropbox, or maintain your collection of files strictly offline. There is a web-brower based version that can be run from a USB drive, and a desktop version for offline use. It's collaboration features are not quite as robust as Mendeley, but you can create online groups to share references, follow individuals, and search and browse for both papers and people.
Note: Zotero is a production of the Roy Rosenzweig Center for History and New Media atGeorge Mason University and the Corporation for Digital Scholarship. It has been generously funded by the United States Institute of Museum and Library Services, theAndrew W. Mellon Foundation, and the Alfred P. Sloan Foundation.
The Library's Guide to Zotero: