When grouping more than two items, a comma isn't required, but is preferred. For example, I ate three hot dogs, four pizzas, and twenty-two enchiladas today!
You can even put a comma after "and," when adding a somewhat separate statement, like this: The mailman left work and, in order to avoid the evil dog, took the long route home. Of course, this might look odd, but really it reflects the intonation of how you'd say the same statement.
The best way to know when to use commas or not is by saying the sentence out loud, and including a comma where you use a pause while speaking. (Like I did with this sentence!)
Others may have their own opinions; I'd wait to see what they have to say before embracing my thoughts.