BBC In Our Time
There is not much to say but this podcast has some of the most interesting topics in mind. It goes from 25-45 mins with usually two or three guest speakers from universities talking about history, religion, literary critcism, politics etc. It's a good way to be educated in a general sense on wide range of topics in under an hour, also the guest speakers provide a range of different opinions to compare. Take a simple topic and the podcast will plunge the depths of it to see the complexities that popular culture and education does not taken into account. One of the best educational podcasts in my opinion.