Welcome to RTA!
I guess the biggest question one could ask would be: how long do you have for this trip?
By the most *direct route* Orlando to The Badlands (in South Dakota), you are looking at 1900 miles. Driving 4-5 hours per day, that takes you about 7-8 days to go one way. That is the most direct route, though, and not necessarily very scenic.
Interesting places can mean different things to different people. What you might do is open up a US map or atlas and start picking out places more or less between your starting point and ending point and see what interests you. The maps will list national parks, state parks, and occasional fun things, but you may also want to seek out the Map Wizard and other things on this website to see what interests you.
If you want to share with us, what you'd like to see or do on your trip, we can help you. If we know the types of things that interest you, we'll make more pertinent suggestions than just throwing out a bunch of ideas and hoping one idea helps.
Donna