Zotero - Bibliographic Management Tool
Zotero [zoh-TAIR-oh] is a free, easy-to-use Firefox extension designed to help you collect, manage, and cite your research sources, including books, articles, web pages, or images. It allows you to add and attach pdf files and notes for different projects. It conveniently resides right where you do your work—in your Firefox web browser. It requires Firefox 3.0.
To learn more, visit the Citation 101 guide.
Related Pages:
Advanced Finding Tools 
Bibliographic Management Tools