On our last trip (Me, DH, DD7, DS5), we took along several car games (different versions of I Spy!), lots of cd's, where everyone took turns picking the music, and books on CD (of course they were Disney books). We take the I90, I79, I77, I95 route which passes us through 8 states. As we came to a new state border, the kids got to open a gift (new game, book on cd, disposible cameras, spending money, etc). Sometimes it's a long time between gifts, but other times, it is only about 45 minutes (eg. going through Virginia). This seemed to make the trip shorter for the kids as it seemed like several short trips (until there next present) instead of one long one.
We leave at 5:00 am and get to the border in Buffalo at 7:00 am. We make several stops along the way (about every 2 hours) for bathroom breaks, gas or meals. This gives everyone a chance to stretch their legs. Sometimes we will have races to the bathrooms, or once at a rest stop there was a large hill behind the building and we ran to the top and down, just so we could run off some stored up energy. We also have on night in a hotel.
We have yet to use dvd players for the long trip. As long as the kids can find things to do (and enough drinks and snacks), they travel pretty well.