There are a lot more seasoned travelers than yours truly.
That being said, I guess it all depends on what you want.
If you're looking for relaxation, I'd recommend the Black Hills. You can fly into Rapid City, rent a car, and take in whatever you want. One of the most refreshing trips I've ever been on.
If you haven't been to DC, you must before you die. Even if you can't stand what's going on in the buildings, you still need to see it. Take the museums, go to the square and the monuments. It is pretty profound.
But yeah, it really all depends on what you are looking for.