Like most midwestern states, South Dakota offers little to the performance driver asides from long roads which are easy to speed on. If that's your bag, baby, then all of I90 which runs lengthwise will be your playground. For those who prefer spaghetti-like roads rt. 385 in Mt. Rushmore territory is your best bet. A very interesting drive, if not a particularly challenging one, is the stetch in the Badlands NP south of Wall, home of cheesy trinket and souvenir shops.