Mt. Rushmore was meh, but the Badlands really did it for me - I was more impressed with that area than the Grand Canyon. If you're into hokey stuff, there's the Corn Palace in Mitchell and Wall Drug in Wall. The Crazy Horse memorial will dwarf nearby Mt. Rushmore when it's done...eventually. Wild West and dinosaur attractions etc - enough to do to keep you busy for a number of days and get it off your list.