Everyone argues about this. I tend to leave it in to avoid the 'ham and cheese' phenomenon. If you're listing sandwich ingredients, leaving out the comma might give you this:
Today's sandwiches:
.....Bacon, lettuce, roast beef, ham and cheese.
Is that last item a ham and cheese sandwich, or can you get a ham sandwich or a cheese sandwich? In this case, there's really no way to know. Also, since one tends to pause when saying the list, it seems natural to indicate that with a comma. Just my two cents worth.
Gaian Grammar Guild
The Gaian Grammar Guild is a refuge for the literate, a place for them to post and read posts without worrying about the nonsensical ones.