APA StyleNot as complete as the Manual, this site still offers a lot of information about using APA style - not just references and in-text citation, but also paper format, tables and format, bias-free language, and other topics. It's been updated to conform to the 7th edition, so don't rely on this site if you're supposed to be using the 6th.
Publication Manual of the American Psychological Association (APA), 7th ed. by