Hi Leslie,
I birded 5 Australian states last Sept/Oct and found the best guide to be The Slater Guide to Australian Birds by Peter, Pat and Raoul Slater. It is small enough to carry in your backpack and comes with a plastic cover, so it won't get damaged out in the field! It also includes all the relevant facts, distribution maps, full-colour illustrations and best of all - a visual index where you can quickly determine the major bird family and then go straight to the corresponding pages without wasting much time.
Australia is truly stunning, goodluck with your trip planning!
Andre