Stephen B. Smith, a political science professor at Yale University since 1984, has made available a 24-lecture course, Introduction to Political Philosophy, which covers Plato, Aristotle, Machiavelli, Hobbes, Locke, Rousseau, and Tocqueville.
His approach is highly literary. In his Republic lectures, for instance, he spends a good chunk of the time discussing the metaphors and characters involved. One of Smith's major concerns is what citizenship amounts to. The lecture above is on Plato's "Apology," and while this may be Plato's most famous work (with its dictum that "The unexamined life is not worth living"), it's less about political philosophy than about the virtuous life. Smith sees these topics as intimately related, and in his closing lecture, he gives a defense of patriotism, saying that in the ivy league environment, expressing an interest in patriotism is like confessing an interest in child pornography.
Despite his engaging style, he speaks somewhat slowly. If your listening device offers a "double speed" feature, I recommend using this. You can obtain the whole series on the web: Yale web site - YouTube - iTunes (audio) - iTunes (video). You can also find the course in the Philosophy section of our collection of 1200 Free Online Courses.
Mark Linsenmayer runs the Partially Examined Life philosophy podcast and blog. He also performs with the Madison, WI band New People.