Books and words trump videos with wheels

This could easily come off as me being a product of my generation, but I'd encourage you to avoid using DVDs in the car.  Granted we never had these when you were young, and I'm sure the video player makes an easy babysitter, but there's a lot to be missed by getting into the habit of turning on an in-car video player or hooking one up so you don't have to 'deal with the kids'.  

When you were young, before you could read, on vacations; even the long ones involving 15+ hours in the car; we'd get books on tape and enjoy those for hours on end.  The whole family could participate rather than the kids in the backseat silently watching a video.  Getting everybody to participate also allows for conversations about things that may be misunderstood or just plain provide opportunities to interact.

If I recall this story correctly, on one long trip (again a 10+ hour car ride), we'd listened to a book most of the way home and when we arrived home we sat in the car in the garage for another 20 minutes so we could hear the conclusion of the book.  Good fun and a good story.