Zotero

Zotero is free Firefox extensions to help you collect, manage, and cite your research sources. It lives right where you do your work in the web browser itself.

Features include automatic capture of citation information from Web pages, storage of PDFs, files, images, links, and whole Web pages, flexible note taking with auto save, fast, as-you-type search through your materials; and playlist-like library organization, including saved searches (smart collections) and tags.

Requirements:

Mozilla Firefox 3.6