In some areas in Australia, there is only one electricity provider and another one gas provider. In some cities, e.g. Sydney, there are many electricity and gas providers. Where there is more than one provider, some providers offer discounts. Moreover, these discounts are negotiable. It is recommended that you call the service providers in your area and negotiate a deal.

Please, note that most (if not all) providers include the discount in ONLY the contract period (usually a year or 2 years). After the contract finishes, they will charge you the full price. You need to call them at the end of your contract and negotiate a new deal.

There are many websites, which provide a comparison between the service providers. However, please note that these websites compare only some providers, with whom they have partnership agreements. There are other providers, who might not be included in the comparison. These websites include iSelect.com.au and CompareTheMarket.com.au.

Recently, the government created a website to help you compare Energy Providers. 
https://EnergyMadeEasy.gov.au/

I came across the following article about Energy Bill Comparison Sites. It has some interesting information.