The Stuart Highway is the highway from Darwin to Adelaide, with a bloody 2800 km long and dull drive accross the desert. Highlights along the 5 day route are pretty much limited to 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.