Zotero (pronounced "zoh-TAIR-oh") is a program that collects, manages, and cites research sources. It's easy to use and it's free.
Zotero allows you to attach PDFs, notes and images to your citations, organize them into collections for different projects, and create bibliographies.
It automatically updates itself periodically to work with new online sources and new bibliographic styles.
Zotero: A Guide for Librarians, Researchers and Educators by 
This guide is created by Jason Puckett and licensed by Georgia State University Library under a Creative Commons Attribution-Noncommercial 3.0 United States License.
You may reproduce any part of it for noncommercial purposes as long as credit is included. I encourage you to license your derivative works under Creative Commons as well to encourage sharing and reuse of educational materials.