This thread on Metafilter discusses some intellectually-stimulating podcasts. I have personally found a lot of great content being podcasted--both by folks who are professionals and those that are amateurs. By amateur, I mean, they aren't regular talk-radio personalities. I have found a lot of food/restaurant/cooking podcasts I like. With the advent of AppleTV in my home, I have also found listening and watching new podcasts much easier. Sometimes podcasts are more interesting because they come from amateurs, or they aren't constrained by the influences that constrain normal radio and television programming. In the back of my head I'm considering a podcast project that's aimed at educating.. I'll let the ideas percolate a bit before saying more.