Victoria :

-Bogong High Plains : although there are several good lookouts on what's called the "Great Alpine Road", to me the Bogong High Plains Road is far better. There's just something about this place, especially in the morning with the cold fog on the Rocky Valley Storage. Compared to the Alpine Rd, it's also less popular, which makes for a more relaxed trip.
-Beech Forest Road : the road between Beech Forest and Forrest in the Otways is a bit of a secret. It's narrow, winding, and limited to 40 km/h. But to me it's the best forest sealed road in the state. You're surrounded by the Otways in all their glory, and nobody takes this road.

-Wilsons Prom' : no, it's not the road to Tidal River, which has only one or two lookouts toward the sea, it's the Five Mile Road. It's only a couple of km, but take it 1 or 2 hours before sunset, and it's alive with kangaroos, wallabies and wombats, near a swamp. A perfect and relatively unknown wildlife spot. Don't miss the easy short walk to Millar's Landing, it's my favorite spot in the Prom'.

-Natimus-Frances Rd : the section between Goroke and Natimuk gives you great views of Mitre Rock (which you can easily climb) and Mt Arapiles (this one you can drive to the summit).

-Pink Lakes Drive : Murray-Sunset is one of the most beautiful places in Victoria, and driving to those gorgeous pink lakes may be the main reason why.
Not on the list : why isn't the Great Ocean Road on the list ? Well because it's usually packed on week ends, because the driving speed limit is ridiculous, and because the best spots are actually at Cape Otway, where it's not the Great Ocean Road anymore. Yes the Port Campbell NP rock formations are amazing, but you can't see them from the road.
NSW :

-Mungo Drive : although taking a tour with a ranger is a must, the self guided drive is also very nice, passing very different landscapes, from scorched land to lightly forested area and red soil.

-Cobb Highway : although a very boring and tiring drive at times, the section between Wilcannia and Hay has some very interesting areas, from red earth to strange wetlands, and the long unsealed section is also pretty fun to drive.
Tasmania :

-Western Explorer : a car ferry river crossing, beautiful forest, some distance signs still in miles, and the beautiful coast before Arthur River make this one of the best drives in Tassie. Some say it's dangerous because of some tight corners, but it's fine, especially considering you won't see many drivers.

-Pirates Bay Drive + Blowhole Road : this one isn't exactly secret, and at times crowded, but as a day trip from Hobart it's great. Easy walks to the main geological formations (loved the Tessellated Pavement), great views of the ocean.

-Gordon River Rd : a classic, to discover the peaks of the SW, to admire the big lakes, and to do your first roadkill at night.

-Highland Lakes Road : the only A road in Tasmania with an unsealed section, it's also quite scenic. The first bit South of Deloraine gives you some glances of the nearby peaks, while the elevated flat section on the plateau has some good lookouts. Next you get some nice views of the Great Lake from the planes or from a dam.

-Stanley Highway, and pretty much all the roads next to Stanley : a great small peninsula to explore, with one of the best towns in Tassie.
There are also some nice roads next to Cradle or at Freycinet but I only put my favorite ones. I'm sure there are great ones on Bruny Island or South of Lauderdale, but I haven't been there yet. Your turn now.