These toolshelp you manage your research, collect and cite sources, and create bibliographies in a variety of citation styles. Each program has its strengths and weaknesses, but all are easier than managing citations manually!
Zotero - free plug-in that works exclusively with the Firefox browser: keeps copies of what you find on the web, permits tagging, notation, full text searching of your library of resources, works with MS-Word, and has a free web backup service.
RefWorks - free for UC Berkeley users. It allows you to create your own database by importing references and using them for footnotes and bibliographies. Use the RefWorks New User Form to sign up.