General Guides
Citing U.S. Government Publications - an excellent guide from Indiana University - Bloomington.
Basic Legal Citation - a guide to citing legal information (cases, constitutions, regulations, etc.), from the Legal Information Institute at Cornell University Law School.
Reading a Legal Citation - a guide from California State University, Stanislaus.
MLA Style
MLA Style - a guide to citing government information sources using MLA Style, created by the Clark Library at the University of Portland.
APA Style
How to Cite US Government Documents in APA Citation Style - created by Cornell University Library.
Citing Legal Materials in APA Style - a guide from California State University, Stanislaus.
Citing Government Sources using APA Style - a guide to citing government information sources using APA Style, courtesy of Washington and Lee University.
Bluebook
Bluebook Guide - from Georgetown University.