Citation!  Shout it out!  Don't memorize it, use these helpful sites to help you prevent yourself from plagarizing.  (Hearty handshake to the first person to successfully diagram the previous sentence.)

Bedford St. Martin's Citation Guides 

http://www.bedfordstmartins.com/online/citex.html

This has guides to MLA, APA, Chicago and CBE writing styles.

Bartleby 

http://www.bartleby.com

Beware: Bartleby.com is a powerful, powerful database.  The reason it is on this page is that it has a comprehensive collection of Strunk & White's styles guides.