Optus - mobile broadband deals. $219 for 72Gb of data; $54 for email+more for a year
1. For $19.95 per month you get 2Gb of data *plus* 4Gb of off peak data per month. Order online and the first month is free. So for $219.45 (11*$19.95) spread out over a year you get up to 72Gb of data. If you go over your data allowance, you don't get hit by excess charges but instead get restricted to the sites listed in the second deal below.
2. For $4.95 per month you get "Unlimited access within Australia to Facebook | eBay | LinkedIn | FourSquare | Twitter | MySpace | Optus Web Mail | My Zoo". Again, order online and you get one month free. So for $54.45 if all you really need is mobile email access (and you can forward your existing emails to the optus email and/or you don't mind switching), perhaps twitter and a few other of these services then this is pretty sweet. The Optus Zoo website is a little cluttered (http://www.optuszoo.com.au/) but does have a lot of content like news, weather, tv guide, etc so there's some value there.
*update* It seems a little confusing if the deals include the standard E160 modem or if you have to pay for a modem..... it's ok but a little less appealing if the basic modem isn't included....