I don't have a specific driving song. When I go on long car trips, I end up picking 3 of my CDs, different moods. Alanis when I want to sing along, my mixed techno/dance CD when I want to just be awake and be jolly during the trip, and a rock CD for in between (rocking and singing).
I just put on my favorite radio station and listen to them, I use to put in CD's but I dont do much of that anymore. It's very rare that the station I listen to will play a song that I dislike, which is why I leave it on that station all the time.