Possible Duplicate:
Should I put a comma before the last item in a list?
How do I know if I need to add a comma or not before a conjunction preceding the last item in an enumeration?
For example, which of the following sentences is correct?
I have a house, a car, a bicycle, and an airplane.
I have a house, a car, a bicycle and an airplane.
Are there any free online references on this matter (with examples, if possible) for the layman?
