Citations are a necessary component of academic research. Citations not only spare us from accusations of the dreaded "plagiarism," but even more importantly they allow the reader (and your professors!) to fact check your information. How do we know what an author says is true? We do so primarily by the citations researchers use to support their argument. This is what makes scholarship scholarly!
The Online Writing Lab at Purdue (OWL Purdue) - Excellent resource. In addition to their up-to-date versions of the most popular citation styles, they also host a number of helpful handouts dealing with writing and grammar.
Citing government information - A helpful site from West Texas A&M on citing government information.
Citing laws - Introduction to Basic Legal Citation from Cornell Legal Information Institute
ASA style guide, 2nd ed. by 
The Craft of Research by 
Student's Guide to Writing College Papers by 
AMA Manual of Style by 
A Manual for Writers of Research Papers, Theses, and Dissertations, Ninth Edition by When Kate L. Turabian first put her famous guidelines to paper, she could hardly have imagined the world in which today's students would be conducting research. Yet while the ways in which we research and compose papers may have changed, the fundamentals remain the same: writers need to have a strong research question, construct an evidence-based argument, cite their sources, and structure their work in a logical way. A Manual for Writers of Research Papers, Theses, and Dissertations--also known as "Turabian"--remains one of the most popular books for writers because of its timeless focus on achieving these goals.
MLA Handbook by Relied on by generations of writers, the MLA Handbook is published by the Modern Language Association and is the only official, authorized book on MLA style. The new, ninth edition builds on the MLA's unique approach to documenting sources using a template of core elements--facts
Publication Manual of the American Psychological Association by
