Serial Comma,,, 1,2, and 3?

The serial or oxford comma is the comma before "and" or "or" in a list of three or more items. I have always omitted this comma, but I have come to learn that this is largely a popular media (e.g., newspaper) thing. There is not written rule on weather or not to use one in a list, however, it has become the convention to use it to add consistency and clarity. Per usual, Grammar Gril has the final say,
"Consider this sentence: I went to see Zack, an officer and a gentleman.
Without the serial comma—I went to see Zack, an officer and a gentleman—it could mean that Zack is both an officer and a gentleman, or that I went to see three people: Zack, an unnamed officer, and an unnamed gentleman.
With the serial comma—I went to see Zack, an officer, and a gentleman—it could still mean two different things. It could mean I went to see three people (Zack, an unnamed officer, and an unnamed gentleman), or it could mean I went to see two people (Zack, who is an officer, and an unnamed gentleman)."

Bottom line, use it!

-Grammar Girl