Mendeley is a free bibliographic manager and social network that is easy to use. Import pdfs to make your own searchable library. You can easily make and share folders, highlight and annotate the articles you are using in your research, and access from any computer.
A few databases, like Science Direct, allow you to save directly into Mendeley.
Mendeley also offers a social network of researchers and the option to share your research privately or publicly.
Mendeley creates great in-text citations and will produce a beautifully formatted bibliography with one click.