I'm told The Great Alpine Way, between Wangaratta and Bairnsdale, is quite good.
Black Spur, between Alexandra and Healesville. Or detour to Reefton Spur (Marysville -> Warburton).
GOR, to Apollo Bay, then on to Lavers Hill and return. Return to Melbourne via Forrest and Moriac. Best with an early (7am) start, to avoid all the tourists.
In Tas:
Devonport -> Sheffield -> Mole Ck -> Deloraine -> Longford -> Cressy -> Poatina -> Bothwell -> Hobart.
Hobart -> Triabunna -> Swansea -> Bicheno. Elephants Pass (Chain of Ponds -> St Marys -> Scamander)
Scamander -> St Helens -> Derby -> Scottsdale -> Launceston.
All absolutely brilliant roads.