The Stuart Highway is the highway from Darwin to Adelaide, with a bloody long 2800 km dull drive across the desert. It goes pretty much straight through the Devil's Marbles but apart from that highlights along the 5 day route are pretty much limited to Uluru (Ayers Rock), Australias most famous tourist trap. Turn into Highway 4 at the Ghan gas station, its a 1 day detour (~300km each way). Avoid the Dirt road to south of Hugh towards Highway 4, unless you have a really robust 4WD.
Don't miss the Mataranka thermal pools 100km south of Katherine for a refreshing bath. Also, getting closer to Darwin are the turnoffs for both Kakadu and Litchfield National Parks.