Hey there great to hear about your pending Aussie adventure.
I'm down south in Victoria, I've visited a few of the sites down here...
There is the Great Ocean Road west of Melbourne. Down there you will find The Twelve Apostles which are definately a 'must see'. There are also other great sites down there such as blow holes and historic sites. A bit further down near Warnambool is a large volcano, though not active it still has a largish cone to explore. There are also tours of sunken ships down that coast if you are into that kind of thing.
Ballarat is touristy but worth a visit. Sovereign Hill is a well put together theme park up that way depicting life in the goldfields. There is also another smaller place called Kryal Castle.. my advice is to pass that by- it's not the place it once was! If you like the historic sites in Ballarat there are some similar ones in and around Bendigo further north.
Also out that way are mineral springs and spas at Hepburn Springs. The town itself has turned into a little New Age Village with all the tourist money that's gone into it over the last 10 or 20 years so it's a fun if not interesting place to wander through. And the hot spas down the road are just to die for.
A bit closer to Melbourne on the western side is the Organ Pipes National Park. It is a steep but short walk down to a gorge with rock walls resembling as it is named organ pipes, a great sight to see.
Further out and more remote are the Grampians which is a gorgeous mountainous area with lots of walking tracks and a great place to camp.
Just north of Melbourne is Hanging Rock. I don't know where you can put your caravan up ther but the Rock itself is worth a visit and the climb isn't too strenuous.
Further north is Glenrowan, a small town with historic meaning. Very very touristy, but not too far off the main highway if you're travelling the straight way between Sydney and Melbourne. It's worth a look if you aren't too put off by the tacky dummies and painful motorised re-enactment thing they have there.
There is a mini museum that isn't too bad for example if you can get past the rest.
South of Melbourne the Peninsula is a nice place to visit in the summer and there are tours at Point Nepean right up the top, as well as a ferry across the bay where you can watch dolphins swimming along with you if you're lucky.
Further east of Melbourne is Phillip Island, another tourist trap. The penguin parade is another 'must see' event down here. And though it's not as intimate the Seal Rocks are worth a visit as well. You might want to stay clear when the motorbikes are racing down there though.
Further east again is Wilson's Promontory which again is gorgeous wilderness and well worth visiting. Keep going east and you'll find the Gippsland Lakes and 90 Mile Beach which again are places to visit in summer. Further inland are the Bucchan Caves which are also fun and have tours every day. North of Gippsland is the Victorian High Country which is gorgeous too with some historic places to explore but very remote with only small towns dotted through it.
Melbourne itself has a large museum and zoo. There is Healesville Sanctuary just east of the suburbs, and Scienceworks in the western suburbs. There are two major art galleries within walking distance of each other in the centre of Melbourne. Southbank is a little shopping metropolis on the south side of Melbourne's Yarra River which also has ferries and floating restaurants going up and down it daily. There are also street performers to keep you from getting bored at Southbank and the City Square both. The Crown Casino is also nearby which I can recommend for one reason only and that is the spellbinder foyer display. Close by also are the Melbourne Aquarium- though I have never been there so don't know if it's worth visiting.
The Melbourne Migrants Museum is
close by too and that is
If you want a bit of Aussie culture come in September and go to one of the AFL final matches at the MCG or Docklands.
Hmm, maybe I should apply for a job at the Victorian Tourist Bureau.
Hope some of this info is useful to you.