Road trips are fun, but after a long enough time in the car, even the most die-hard road trippers are bound to get a little bit of highway hypnosis. If you have satellite radio, tune into your comedy station and listen to some stand-up. It'll keep you actively listening and laughing way more than music. If you don't have a comedy station available to you, purchase a few humorous books on tape (I recommend anything read by David Sedaris). It's as good as stand-up for keeping you engaged, and you can usually rent books on MP3 or CD for free at your local library.