I ended up downloading a couple full-length Bill Maher podcasts--basically just the audio of his TV show. Listened to one on the way down yesterday and laughed myself silly (his main guest was Larry King). I have another to listen to on my way back up on Monday. I also got some episodes of NPR's Planet Money, which seems pretty cool--all about economics. I got some RadioLab and The Moth, both of which were suggested to me by friends. An episode of the BBC's Arts and Ideas (I was listening to that one when I got pulled over for speeding in Iowa--sigh. 80 on the Interstate is such a crime??)
There's a lot of good stuff out there! Makes driving for 7 hours much more pleasant than listening to the same old song playlists over and over.