If you don’t know what PodCasts are - they are basically audio (or video) files which are stored on a server so that you may download and listen to (or watch) them for free at your convenience. There are radio programs, university lectures, literature readings, forum discussions etc - basically whatever you are interested in, there are bound to be dozens of PodCasts about it, be it architecture, iPhone programming, science, religion, movies, fashion etc etc.. Especially interesting are lectures, seminars, and courses put out by Universities like Stanford, Berkeley, and MIT.
The best PodCast I have ever heard - easily followed, interesting, and very very funny - is a lecture by Robert Sapolsky about “Why Zebras don’t get ulcers”
Other PodCasts I highly recommend (most of them are weekly PodCasts):