Printed style guides are in the Citation Style Guide Collection by the reference desk.
Chicago (Reference Z253.U69 2003)
For humanities (e.g. literature, history, arts).
MLA (Reference LB2369 .G53 2003)
For languages (e.g. English, Spanish, German).
Scientific Style & Format (CSE) (Reference T11.S386 2006)
For biology & general sciences. Also known as the Council of Science Editors (CSE) and formerly as the Council of Biologist Editors (CBE).
Citing Internet Resources (Reference PN171.F56 L5 1996)
This guide fills in the gaps of other style guides when dealing with online resources. If your other styles guide doesn't mention how to cite an online source, try this.
Zotero is a free, open source browser app that collects, manages, cites, and shares your research sources. It lives right in your web browser, and has a similar design to the iTunes library.