Gary Wills and Michael Lind come to mind as conservatives who defected; Lind, however, still wrote a great book defending the US war in Vietnam. Lind is more of a old-style liberal, not a member of the New Left. Wills is another creature altogether.
Welcome aboard, Mr. Mamet.
bump
Others- David Limbaugh, Tammy Bruce
Sorry- not David Limbaugh- David HOROWITZ!