If you are a member of the Punctuation Police, you will enjoy this sample of punctuation guides. Depending on your profession, some style guides are more important than others. For example, if you are in the legal profession, you would look to the Bluebook for specific rules on punctuation.
Another source of multiple style guides, including rules on punctuation and grammar, can be found at http://www.RefDesk.com under http://www.refdesk.com/topgram.html and Library Spot, Grammar and Style, at http://www.libraryspot.com/grammarstyle.htm. -CCE
The Punctuation Guide
Tips on Grammar, Punctuation and Style
Harvard College Writing Center
Punctuation and Style: A Quick Reference Guide
Office of Communications, University of Puget Sound
Introduction to Basic Legal Citation, by Peter Martin, Cornell University Law School, Legal Information Institute (not just for legal citations – CCE)