Here you will find weekly planet.osm extractions for Australian states.
The files are in Garmin .img format, and are loadable into Garmin GPS receivers using tools such as sendmap.
Click here to go straight to the download page.
Click here for credits and some info on how this was done.
If you're after some map transfer hints, see here.
While there are other mapping efforts in Australia, they all have problems such as having a closed development model, restrictive licencing or are just plain difficult to update.
OSM avoids these problems by using a creative commons licence, and having mature tools for anyone to use to update the data.
Remember - many hands make light work and many eyes make the data accurate, particularly when the map creators have local knowledge – so get mapping (but before you do, read the Australian tagging guidelines here).
A good visual representation of how OSM is growing can be found here.
Due to its openness and ease of use, I am certain that OSM will become THE map data repository over time.
APRS - Amateur Radio killer app