Ok, well the ones chosen so far are Summersville Lake in WV, Great Smoky Mountains, the swamps of Louisiana, the Grand Canyon, driving through Death Valley, Yosemite, and Joshua Tree national park. I thought that was quite a varied selection, but it sounds like I'm missing some obvious choices out.
It's all good recommending every national park in the country, but do you have any personal recommendations you'd pick over all the others? It's quite difficult on a trip with tight time constrictions to make time for national parks when I don't have a clue what to go for. With the cities I can go off what I know, and use websites like tripadvisor to check the place out. All I get with national parks is "this national park is great", but no way of determining which ones I should go for, and what makes them unique from all the other national parks.