Im actually heading to NZ and Aussie myself in Dec/Jan for a month... I am flying between Syd and Melb because my friend told me that there isnt much to see between the two cities, but everywhere else...

The cheapest method for domestic travel is: www.virginblue.com, www.quantas.com.au, www.freedomair.com.

Note: if you are going to quote from quantas, check their webdeals! thats where the cost savings start. make sure you go to the "au" website otherwise you wont be able to book. if you want to do the conversion back to USD you can try www.xe.com for exchange rates. typically the AUD is bout 25% off...