Here are a few websites that you may find useful.
Australian Taxation Office
Information on obtaining a tax file number so that your income tax is deducted at the correct rate.
Australian Government - Department of Immigration & Citizenship
The Department of Immigration and Citizenship has information on work permits and visas. You can even submit your application online!
Second Year Working Holiday Visa
Information for backpackers on how to qualify for a Second Working Holiday Visa.
Our default superannuation fund for casual employees is PrimeSuper.
Departing Australia Superannuation Payment
This link to our default superannuation fund (PrimeSuper) provides information on how members such as backpackers and others returning overseas can apply to get their employer's compulsory superannuation contributions made on their behalf returned.
For backpackers - they will help you (for a fee) get your tax and your superannuation back when you finish working in Australia. There are other companies also that offer similar services.