Mendeley is a free research tool that enables you to manage citations and PDFs using a desktop client or through your account on mendeley.com.
Mendeley has drag and drop capability to integrate PDFs and other documents into the program.
Mendeley also includes plugins for Word or OpenOffice, so you can easily create citations and/or bibliographies as you write your papers.
Mendeley includes social networking tools as well. You can share your research, discuss topics with other researchers, and search for new information through the site.
