The Basics of APA Style
A tutorial made by APA, explaining the basics of the APA style

APA Style Help
Official help-page of APA, with frequently asked questions

American Psychological Association (APA) Style Examples 
Made by the Monash University Library in Australia

APA Formatting and style guide
Part of the Purdue University Online Writing Lab (OWL)

Chicago Manual of Style Online
The online version of the Chicago style

Chicago (notes-bibliography) style examples
Made by the Monash University Library in Australia

Harvard (author-date) style examples
Made by the Monash University Library in Australia

Quote, Unquote: A guide to Harvard referencing
Made by Leeds Metropolitan University 

MLA Formatting and Style Guide
Part of the Purdue University Online Writing Lab (OWL)