MLA (Modern Language Association) style is most commonly used to write papers and cite sources within the liberal arts and humanities.
APA (American Psychological Association) is most commonly used to cite sources within the social sciences.
Chicago/Turabian style places bibliographic citations at the bottom of a page or at the end of a paper. The Chicago and Turabian styles are most commonly thought of as note systems.
Harvard referencing is the preferred style of the British Standards Institution. It is used mostly in the sciences and social sciences.
Oxford style is also referred to as the documentary-note system.
The Vancouver style that was initially developed by an international committee of medical journal editors meeting in 1978 in Vancouver.
CBE (The Council of Biology Editors scientific style of documentation) is used in the biological sciences and many other fields of scientific study as well.