Over at the BBC, Melvyn Bragg presents a weekly radio programme called In Our Time in which are discussed a wide variety of subjects ranging from art and philosophy to politics and drama. Surprisingly, considering the wide range of human culture covered, Bragg devotes a good proportion of episodes to mathematics. He’s just presented a programme on the Negative Numbers and recently presented one on Prime Numbers. If you dig into the science archives you’ll find recordings of programmes on Zero, Infinity, π, Chaos Theory and Renaissance Mathematics. Some of these are conveniently available as podcasts.
(Note that some of the comments about the mathematical topics on the In Our Time website are a little inaccurate, eg. “a team of researchers…calculated the highest prime number”, but the actual guests on these shows are generally mathematicians or historians of mathematics who know what they are talking about.)