From OCAU Wiki
The easiest way to send a parcel within Australia is using the postage service provided by Australia Post. They have thousand of outlets across the country and even deliver right to your front door. Friendly staff at the Australia Post outlets are more than happy to help with any enquiries you may have in regards to your postage needs. Australia Post also maintain a very informative website.
Australia Post does not hold a monopoly on the postage market. There are many more companies that specialise in delivering your precious parcel to any address in the world. Indexes like google.com or yahoo.com may help you find them.