3 has unveiled a brand new plan that offers 6GB of mobile 3G data for just $39/month. The offer will, however, require you to get a 24 month contract with the telco. However, it does come with a USB dongle, so you can use the 3G network on your laptop.
While it beats the previous "king" from Vodafone, which had 5GB for $39, it does not have better coverage than its competitors, but less. And if you are ‘unlucky’ to go out of the area and roam into Telstra’s territory, also known as their GSM network, you will pay fees of $1.65/MB.