This site www.adioso.com is the best around for finding the cheapest airfares between Australian airports and those served though Asia by Tiger, Air Asia and Jetstar.
The advantages of using this website is that it will display all airfares between destinations for the next three months in both fare and date order. The search flexibility is unending. e.g. Darwin to anywhere in Australia, or Melb to Cairns late June, or Perth to overseas, etc etc. The indicated fares have taxes and charges already added. Once a flight is selected the return fares are viewable via a drop-down box (for about the following 30 days). This site beats Webjet hands down because of its broad range of options. It transfers you through to the airline website to book as you would normally. This ensures that you will be able to take advantage of any last minute specials that your chosen airline may be offering. I love this Australian site so much I sometimes use it for "virtual travel" :)