These three sites are very helpful, when searching for your soldier ancestors.
Australian War Memorial; this site has so much on it and is easy to use. The Search for a Person is great and there are links to the Commonwealth War Graves Commission and the National Archives of Australia.
National Archives of Australia, is another useful site, but it does take a bit of searching to narrow it down, but sometimes you find a gem, hidden in the broader search.
Discovering ANZAC’s is relatively new and has similar information, that the War Memorial and National Archives have but is well worth a look. Be creative with your spelling as they have sometimes misspelt surnames.