APA Style is from the American Psychological Association. It is a very widely used style in the social sciences--not just in psychology. It is probably the most commonly used style on campus.
Covers all aspects of creating a paper using APA formatting (6th ed.), citations, and reference list. Also provides help with grammar and punctuation. From the University of Wisconsin-Madison.
Use this list of common questions about references, punctuation, grammar, and style to get official answers directly from the American Psychological Association itself. For help with specific citation examples, use one of the other sites.