You can buy some tickets over the Internet, if you know exactly what you want, but to get a good idea of the choices available, you may need to talk to a travel agent or to airline reservations staff. Most regional airlines within Australia, and many international carriers, are associated with either Ansett or Qantas. Their best prices are for tickets available only over the Internet. Check websites or other travel information for places of interest to see which ones have scenic flights available. They also do fishing trips.
Some organisations operate air tours of one to several days' duration, often in small planes.
Go to the Destination Map page on their site and click on a destination for details of the trip, prices, etc. Pilots may also be able to make arrangements with a local flying club to rent a small plane.