The Oxford Comma
First of all, what is the Oxford comma? The Oxford comma is the comma that precedes the conjunction before the final item in a list of three or more items. About.com states that The Oxford comma exists because editors and printers at Oxford University Press have traditionally used it.
Most style guides are strongly in favor of the Oxford comma. The Associated Press Stylebook (2010), however, suggests that we, “Use commas to separate items in a series, but do not put a comma before the conjunction in a simple series: The flag is red, white and blue. He would nominate Tom, Dick or Harry.”
So, unless you’re writing for a newspaper in America or following AP format to draft a press release, use the Oxford comma at your own leisure.