As Michael said, you have a nice amount of time but choices need to be made depending on your interests. There are many great National and State parks, City's, historic sites and so on. I would recommend you get a good map of the USA and read around the RTA forums and road trip planning pages above to find ideas. Once you have some dots on the map we can help to join them up and make suggestions and answer any further questions you may have.

Enjoy the planning !