I'd recommend seeing Queensland:
You should defiantly do a trip through North Queensland:
Cairns, The Atherton Tablelands, The Daintree and do a crocodile cruise - they are great), the great barrier reef.
If you were a fan of the late crocodile hunter (Steve Irwin) you can go to the park/zoo = http://www.australiazoo.com.au/
Other than that, you have the city of Brisbane, The Gold Coast, Sunshing Coast, Cooloola Coast - Rainbow Beach (multi colored sand) are interesting.
Haven't seen as much of the other states, tho':
NSW: There is the Blue Mountains, Opera House and other scenic