I will be doing a road trip myself in about another week. I live in the L.A. area and plan on taking Highway 1 all the way to San Francisco. Depending on how many days you have you can either head straight up via highway 1 or the Interstate 5 (less scenic,but faster,) If you plan it right, there are many sights along the way, historical and scenic. My road trip will take a total of 7 days with 3 of them in San Francisco,,,but if I had more time I would probably continue to Napa Valley then to Redwood National Park, then come back down to Yosemite National Park...if you only have a couple of hours then San Luis Obisbo would be a very beautiful drive,,,about a 4-5 hr drive from L.A. with cute little towns along the way. You definatly gotta get outta L.A. for a little bit...it will help you to see why California is such a beatiful state and why we are so intent on keeping it "green."
If you are a member of the "Auto Club" you can get maps and travel guides for free. It has guides for every state and since it is the "Auto Club," there are special road trip sections to help you plan a nice trip.
Well hope this gives you some ideas, have a great trip!