Australia has a massive range of climates, and as such its difficult to be all inclusive. I have lost so many caapi's and other plants to winters and the wrong climate.
Quintessential australian ethno garden, some good suggestions above, but i think if you keep it to Trichocereus of some sort, and Acacia of some sort, catha edulis, brugmansia, datura, artemisia, salvia, and other herbs. lophophora is pretty quintessential.