Bureau of Meteorology

The BoM is the source of all weather forecasting in Australia. Airservices, Weatherzone, Elders, etc all get the data from the BoM and format it to suit their own purposes. If you're preparing a Flight Plan however, you must use the "Official" forecasts obtained through AirService's website. Use the Pilot Briefing link.

Elders Weather

A lot of people swear by Elders Weather for their local forecast. Here's the link to Orange weather, and from there you can link back to state or national forecasts.