I have found that it is quite hard to discover which podcasts are good and which are rubbish. You end up having to listen to some rubbish in order to find he good stuff. So for what it is worth here are some podcasts that I have found to be good.
Scientific American : 60 seconds science subscribe
BBC : In Our Time – looking at thoughts and ideas that have shaped out world subscribe
Infidel Radio : Infidel Guy – Debate Hour – some great interviews on the Philosophy of Religion subscribe
Guardian : Science Talk subscribe
New Scientist : subscribe
Scientific American : science talk subscribe