There are thousands of different citation styles out there. Choosing one depends on where you are submitting your work. Make sure to carefully follow any citation guidelines and be aware that the chosen citation style may also impact other sections of your paper's format.
The NLM citation style is commonly used in medicine. This electronic style guide includes instructions on properly formatting for a number of different material types.
The Purdue Online Writing Lab, commonly called the OWL, contains many resources on writing and research, as well as up-to-date formatting and citation guides. Their ALA and MLA guides are especially popular.
A collection of style guides, citation generators, and information about citation management programs.