It depends a bit what you're interested in; I often listen to By The Well, which is a weekly podcast from a group of Biblical scholars looking at the lectionary readings for the coming Sunday; if you're interested in the development of doctrine, The Road to Nicaea is supposed to be very good (it's on my list to listen to). For reflection on more recent matters, The Rise and Fall of Mars Hill was excellent. I also often listen to the Christian Feminist podcast.
But whatever topic you're interested in, there are heaps out there.