Google Maps has offered traffic information for Sydney, Melbourne and Brisbane since late 2009. Now it has added traffic data for Adelaide and Perth as well.
Like the earlier implementations, the system uses data from Suna to offer a colour-coded general overview of traffic density (green is no problem, yellow has some congestion, red is heavily congested and black you just don't want to know). It's not updated as frequently as dedicated TMC systems as a GPS, but it's a quick helpful check if you want to see conditions on your route.
More road traffic information and better mobile maps in Australia [Google Australia Blog]