General:

Brief Guide to Citing Government Publications
http://exlibris.memphis.edu/resource/unclesam/citeweb.html
via University of Memphis

Citing Government Information Sources Using MLA
http://www.library.unr.edu/subjects/guides/government/cite.html
via University of Nevada, Reno Libraries

General Guidelines for Citing Government Publications
http://www.library.unt.edu/govinfo/browse-topics/citation-guides-and-style-manuals/citing-government-documents#government-document-style-manuals
via University of North Texas

Legal:

Introduction to Basic Legal Citation
http://www.law.cornell.edu/citation/
via Cornell University, Law School
see How to Cite and Examples of Citations

Maps:

Guide to Citing Maps & Atlases
http://library.mcmaster.ca/maps/mapcite.htm
via McMaster University Libraries