We've all heard the famous example of how a serial comma can help disambiguate a sentence:
This book is dedicated to my parents, Ayn Rand and God.Xopher's comment gives a a link to a great new example:
Among those interviewed were his two ex-wives, Kris Kristofferson and Robert Duvall.Language Log also has something to say about this new example.
Despite the fact that the serial comma is standard American usage, and its omission is standard British usage, I tend to use it anyway, simply because it provides less chance of an ambiguous parse (even in less hilarious cases than those above). However, I do follow the British usage that punctuation goes outside the quotation marks when it is part of the quoting text and not part of the quoted text. It's only logical.