.: Not sure how I missed this one, but Nature is offering weekly podcasts since 5 October 2005. From the Nature site:
Welcome to the Nature Podcast. Each week we'll be publishing a free audio show, presented and produced by Chris Smith, a doctor, virology researcher and radio presenter from the University of Cambridge, UK.
Each show will feature highlights from that week's issue of Nature and interviews with the people behind the science, and journalists covering the research.