Australia has never had an R18+ rating for video games, as inconceivable as that notion is. Instead the cutoff has been 15+, with games either being heavily cut or banned outright.
Thankfully, after many years of tireless campaigning by the Australian gaming community, an R18+ rating will soon come into effect. The Senate passed the amendment to the current legislation and the R18+ classification will be in force from Jan 1, 2013.
In the few years since calls for an R18+ rating became so loud they could no longer be ignored there will still groups and individuals arguing against it, but support for its introduction was around 98 percent in 2009.
This change to the law means that games previously banned from sale in Australia could now be reclassified in order to secure official releases. The list is so long it has its own Wikipedia page but includes Manhunt, Mortal Kombat, and Syndicate.