Known as the "APA Manual," this is used most frequently in the social sciences. The manual describes all elements of a research paper, and discusses the conventions of manuscript preparation, including punctuation, quoting sources, tables and statistical material, and the reference list. There is an APA website with tutorials and additional guidelines.
APA follows the Bluebook for citing legal materials.
From CrossRef.org. Look here to find DOIs to complete APA citations for journal articles. DOIs can also be added to Chicago Manual of Style citations.
From Purdue OWL (Online Writing Lab). Sample paper plus lots of examples. Includes PowerPoint presentation.