American Anthropological Association (AAA) style uses The Chicago Manual of Style and Merriam-Webster's Collegiate Dictionary. Check out the Association's free Style Guide here.
The American Chemical Society (ACS) style uses the ACS Style Guide: Effective Communication of Scientific Information. The chapter on References is freely available online. Other guides to check out are UCLA's Common ACS Style Examples or USC's ACS Citation Guide.
American Political Science Association (APSA) style relies on an author-date system and cocentrates on formats of information that are important to political science and those that are produced within the United States government. Click here to access the full-text PDF version of the APSA manual.
American Sociological Association style help is available on the Purdue OWL.