Some podcasts are excellent. Check out radiolab.org

edit: I have family+friends 4 hours away and gf 2 hours away, so I spend a huge amount of time behind the wheel as well. I download courses from iTunes U, OCW or individual universities' web sites. I also follow a few podcasts. The skeptic's guide to the universe is decent, radiolab is great. I'm half way done through Yale's Bob Schiller's "Financial Markets" class, and its been great.