1. Instant runoff voting (preferencing the candidates from 1 to x).
2. Compulsory voting (actually a fine for not visiting the polling station and getting your name crossed off, voting is optional).
The two systems together work to keep everyone involved to a certain extent in the political system, a choice in who you can actually vote for, and historically, stable centralist governments. We have over the last decade or so ended up with less stable governments, but this is more a reflection of a convergence to the centre. The differences between the major parties is now so small that changing does not make much difference in policy.
The one downside is it does make Australia a rather boring place to live :)