Rex Airlines has begun to offer a Backpacker Pass that offers unlimited travel on any flights to destinations across Australia for one to two months. Prices are about $410 for a one-month pass and about about $780 for a two-month pass. Routes link Sydney, Melbourne, and Adelaide with far-flung destinations, such as Kangaroo Island, Ballina, Cooper Pedy, and Broken Hill. For example, here's a sample route between Sydney and Kangaroo Island, which would take 19 hours to drive but can now be reached cheaply by an afternoon flight.
More details at Rex Airlines.