Here are a few places to look into or for others to comment on.
Western Aust Broome,The Last Frontier
Ningaloo Reef, Whale Sharks and Manta Rays
Perth, Beaches
Northern Territory Darwin, Big Crocs, Barra and other things that bite
Queensland Great Barrier Reef, Great Snorkeling/Diving
Gold Coast, Theme Parks
NSW Sydney, Harbour Bridge, Kings Cross (not for the kids)
Bondi Beach, Surfing
Victoria Melbourne, Restraunts
Great Ocean Road
South Aust Adelaide, Restraunts, Beaches, Great White Sharks
Kangaroo Island, Native Animals
Barossa Valley, Wines