From Michael Quinion’s World Wide Words #778 of 3/17/12:
Miles Irving found this in an article on Dalhousie Castle in the Scotsman on 14 March: “The castle was visited by England’s King Edward I, also known as Longshanks, the Hammer of the Scots, and Oliver Cromwell.”
Three contributions to the problem: (a) the combination of a parenthetical or appositive construction with coordination, both of which use commas, but in two different ways; (b) the possible use of asyndetic coordination (lacking an explicit coordinator) in Longshanks, the Hammer of the Scots — it helps to know that these are two epithets for Edward I — though perhaps the writer’s intention was that the Hammer of the Scots is to be understood as in apposition to Longshanks, inside the parenthetical introduced by also known as (one parenthetical inside another is a potentially confusing configuration); and (c) the choice between using the serial, or Oxford, comma or avoiding it. The result is that even if you know that Oliver Cromwell is not an epithet of Edward I, but the name of an entirely different person, you are likely to get hung up on that absurd interpretation.
Some comments on this particular example, then an inventory of LLog and AZBlog postings on the Oxford / serial comma.