I always forget what that optional comma before the “and” in a list of items is. Now hopefully I won’t. (FYI, it’s also called a “serial comma,” which is logical and less forgettable but also less interesting.)
It’s been awhile since I checked my AP Stylebook, but I think AP style is to leave it out unless that leaves the sentence unclear (which makes sense, since space is money in newspapers). My personal preference is always to leave it in (to err on the side of clarity), but I have had to follow house style against the serial comma in all my professional editing days. And, as Wikipedia points out, adding the comma doesn’t always clarify.
I have never felt comfortable omitting the Oxford comma (as I just now learned it is named). Sometime, early in my development, I learned (or believed I learned) that a comma must separate every item in a list, and I’ve never broken the habit. The same goes for double-spacing after a period or colon. I’ve had friends inform me that this is a relic of the days of the typewriter and has fallen out of favor, but I will probably never stop doing it. Interestingly, I only single-space after a semi-colon, although wikipedia informs me that double-spacing (or “English spacing”) can be appropriate at the end of sentences, after colons, AND after semi-colons. Notice the serial comma.