Try Zotero
Zotero [zoh-TAIR-oh] is a free, open source tool that helps you collect, manage, cite, and share your research sources. It lives right where you do your work - in your web browser. Designed to be intuitive and unobtrusive (it looks a lot like an iTunes library), Zotero is a powerful and handy tool for any academic.
Check out this handy Quick Start Guide to get started with Zotero today.