Anything by John Valby ("Doctor Dirty")is, without question, of questionable taste. Australia has Kevin Bloody Wilson, who is as filthy as Valby but with an accent (one of his starts out, "Hey, Santa Claus, you c___t, where's my f____ing bike?").
I've heard through the grapevine that there's a CD coming out in June of uncensored sailor songs. There's bound to be some really inappropriate stuff on that one.