I listen to various shows on my ipod but one that really stands out is Dan Carlins Hardcore History. I had misgivings about it before listening because I figured this guy was going to be like the Nazi-obsessed military fetishists in the front of my history classes back in college, droning on and on about army movements. I was wrong though; hes insightful and thoughtful while keeping the show accessible to laypeople and moving things along. Hes not an academic, which I really appreciate. He writes like he wants people to listen to him, not like he wants them to give him tenure.
New episodes come out every month or so, when theyre ready. His 6-part Death Throes of the Republic series (part 1 here) about Rome is a real standout. It just has everything: big ideas, sex scandal, war in the East, adolescent butchers, triumphs, suicide pacts, class struggle, corruption, ambition, bodies dumped in the Tiber river, conflicting accounts & debt. Id recommend this to anyone whos curious about the late Republic era. The whole thing might give you a pretty negative view of human nature if you thought about it too much. I listen to this when I run here in SF and I sometimes have to stop running while listening and think to myself real talk. I even sent them $10 because I liked the show so much.