I unreservedly recommend Backstory, Skeptoid, Freakonomics, The Ancient World Podcast, and This American Life. Comedy Bang Bang!, Radiolab, and With Good Reason are all usually good but I end up skipping some of them.
If you're going on a long trip, though, and you are a fan of history (especially, obviously, ancient Rome), I strongly suggest The History of Rome by Mike Duncan (http://thehistoryofrome.typepad.com/). It's no longer producing, but there's 179 episodes making up I would guess close to 100 hours of fantastic storytelling.