As I have previously posted, I listen to science podacsts quite a bit. Every Monday I load my iPod with a new fix of science audio updates. My favorite one is and remains "This Week in Science" by Kirsten and Justin. Very entertaining, funny and educational. Close runner-ups are the two podcasts by Chris Smith: The naked Scientists and the Nature podcast. Of course, I do like the other ones as well - why would I listen to them every week otherwise?
But here the prominent feature for This Week in Science: Kirsten and Justin Rock!