The Australian government is getting into the act of making public information datasets available online through data.australia.gov.au. The portal provides access to a variety of government datasets with most concentrated in environmental, community, geographic and transportation areas at the moment. My favorite is a shapefile of all Austrialian World Heritage properties! Many of the datasets have Creative Commons licenses, so feel free to have fun with them.
In fact, the Government 2.0 Taskforce is encouraging Australian users to enter the Mashup Australia Competition. Submit your mashups between October 7th and November 6th. The US version, Data.gov, should take a cue from the Australians and have a mashup competition!