APA (American Psychological Association) - most often used in education, social sciences, and business.
Publication Manual of the American Psychological Association BF76.7 .P83 2012
APA Style Guide from Purdue OWL
CMS (Chicago Manual of Style) - used in humanites and social sciences.
The Chicago Manual of Style Z253.U69 2010
Chicago Style Guide from Purdue OWL
MLA (Modern Languages Association) - used in literature and the humanities.
MLA Handbook For Writers of Research Papers LB2369 .G53 2009
MLA Style Guide from Purdue OWL
Additional Resources:
Model Papers by Diana Hacker - view sample papers written in MLA, APA, and CMS
Ask your professor which style is preferred.
Remember to be consistent with your style throughout your work.
Check out the different style guides listed below to help you.
The Writing Place can help you with your paper writing. Don't forget that a librarian is happy to help you both with finding and citing sources.