Washington, Colorado, the Grand Canyon, Vegas, Phoenix, drive the coast from Seattle on down... There's just too much to see. What interests you? Do you have GPS so you can hit out-of-the-way places? I agree with Jessica, stop at anything that catches your fancy and don't be in a hurry.
I've done too many road trips. Dress comfortably, don't get fancy. Pull over every few hours and get out of the car and walk around a bit. If you feel sleepy, don't push, get a room and sack out.