Jetstar has a pretty reasonable sale on at the moment. Flights valid for various periods between 27th Jan and 23rd June, however some destinations have blackout periods which you can see on the Jetstar site.
Sale ends 17th November so be quick!
Brisbane Christchurch - $149
Brisbane Denpasar (Bali) via Darwin - $299
Cairns Tokyo - $199
Darwin Denpasar (Bali) - $199
Darwin Ho Chi Minh City - $229
Darwin Singapore Only on JQ61/62 - $149
Melbourne (Tullamarine) Bangkok - $369
Melbourne (Tullamarine) Christchurch - $149
Melbourne (Tullamarine) Denpasar (Bali) - $349
Melbourne (Tullamarine) Tokyo via Cairns only - $328
Melbourne (Tullamarine) Singapore via Darwin - $249
Gold Coast Auckland - $159
Gold Coast Christchurch - $149
Gold Coast Osaka - $269
Gold Coast Tokyo - $269
Perth Jakarta - $149
Perth Singapore - $169
Sydney Auckland - $159
Sydney Christchurch - $149
Sydney Denpasar (Bali) - $349
Sydney Phuket - $389
Sydney Honolulu - $299
Sydney Osaka via Gold Coast on JQ19/20 only - $369
Sydney Tokyo via Gold Coast on JQ19/20 only - $369
Sydney Ho Chi Minh City via Darwin - $249
As for Japan flights, I have seen better pricing (i.e. SYD-Osaka/Nagoya $349 or even $299) before so it's not the best one and considering the recent sharp crude oil price drop, they should be able to give us better price than this (I believe they haven't changed surcharge yet) having said that, I thing it's a 'sale price' compared to normal 'standard' fare though. I pass and will wait for a better one in the future.