Zotero is a free, open source extension for the Firefox browser. It enables users to collect, manage, and cite research from all types of sources. It is easy to use, lives in your web browser where you do your work, and it is free! Zotero allows you to attach pdfs, notes, images and screenshots to your citations, to organize them into collections for different projects, and to create bibliographies using Word or OpenOffice.
The Zotero LibGuide, created by Merinda Hensley, walks you through using Zotero to manage your citations.