I use a combination of Open Street Maps (through a program called ViewRanger on my android phone) and Hema maps on Memory-maps.
As the other guys said, Open Street maps is free and it is just a matter of finding the program you are comfortable using it with (ViewRanger is free as well). Memory-map is free, however I had to pay for the Hema maps - I bought the east coast region which surprisingly covers the east coast, from the Cape Yord to Victoria including outback qld and nsw, with the cost here (
http://memory-map.com.au/digital-maps/topographic-maps-australia/hema-maps-australia-4x4-maps.html). The good thing is you can download a free trial and see if you like it.
I like the Hema maps for research, good for driving on the highway as gives distances to next town, can look for alternate routes easily and is relatively east to use and does not require data connection. I prefer using ViewRanger for logging tracks, can choose maps with contours and some 4wd parks and state forest tracks are on there as well (no grading of tracks though)
That is my 2 bobs worth.
PS. And I can be running the 2 programs at the same time on my phone so I can switch between them as I need