Style guides from the Temple University Writing Center:
Another great resource for APA, Chicago, and MLA styles is Purdue OWL.
Other styles common for the sciences and, specifially, physics are CSE and ACS:
RefWorks is a web-based personal database for storing, organizing, formatting, and sharing your citations.
Even though RefWorks and other similar programs will format your citations for you, they're not perfect and you should always double check that everything looks right.