Telstra Elite Mobile Wi-Fi

Telstra Elite Mobile Wi-Fi costs $129 and comes with 5GB of data to use within 90 days.
It's a step above the Optus/Vodafone/Virgin Mobile prepaid Wi-Fi modems, because it supports network speeds up to 21Mbit/s -- which results in real-life speeds up to 8Mbit/s.
You won't see these speeds on Optus or Virgin's mobile networks, as their networks top out at 7.2Mbit/s, and in reality, you'll generally only see speeds of 3Mbit/s at best on them.

Telstra's new 3G Wi-Fi modem connects laptops, i Pads to the net while travelling

Unfortunately, the prepaid mobile broadband recharge plans are almost as expensive as the modem itself — for example, a 6GB plan with 90 days expiry costs $100. The best value plan is the 10GB plan for $150 which stays valid for a year.
The full list of Telstra prepaid mobile broadband recharges are:
$20 Up to 250MB, 21 days expiry.
$30 Up to 700MB, 30 days expiry.
$40 Up to 1GB, 30 days expiry.
$50 Up to 3GB, 30 days expiry.
$80 Up to 4GB, 60 days expiry.
$100 Up to 6GB, 90 days expiry.
$150 Up to 10GB, 1 year expiry.
If you want to unlock the Telstra Elite Mobile Wi-Fi to use with overseas SIM cards while travelling, it'll cost you $100.