Prepay simcard for data in Australia

I don't have enough rep to upvote Enchanter Thunderbirds answer, nor comment, but I did the calcs and Woolworths Mobile prepaid sims (http://www.woolworthsmobile.com.au) are the best value as at April 2013. You end up with the same talk time as amaysim which is the other cheapo, but you get more data. Way more data. 5GB. I was there for a month and had over 4GB left. The sim is $2 and the top up is $29 ish. You can get them from any Woolworths supermarket or the smaller ones (used to be Bi LO shops). Easy peasy. The Woolworths sims also use the Optus network which isn't too bad even in regional areas (I was at Scott's Head, NSW for 2 weeks and had no issues).

savvymax and lebara-mobile are two smaller providers. lebara-mobile is good for calling overseas, savvymax credit does not expire. they don't work in the outback.

2 years ago, I got a Vodafone SIM card with a prepaid 1GB / 1 month plan and a SIM-locked 3G USB stick for 100 AUD. There's probably a similar plan available without the hardware for less money. I got it in a phone store in downtown Sydney, not sure about the airport.

Reception varied a lot, of course; I sometimes had to make do with GPRS speed, but didn't get a signal only where one would expect that (i.e. in the outback or national parks).

Note that activating the card had me going through a fairly complex online registration process (IIRC you could use the card itself for that) which required a valid Australian post address (I used the hotel's without any problems).

As was mentioned already the major two carriers in Australia are Vodafone and Telstra. Also there are two smaller ones like Virgin and Optus. While the smaller carriers offer some times cheap plans, their coverage is lacking.

When I was in Australia in October 2011 I decided to go with Telstra. I don't remember exactly why, but maybe because they were cheaper.

Data plan was an important factor for me and I was very happy with their service.

I bought the sim for 30AUD which you get back as balance on your account. For the same amout I bought a plan that included data & call minutes. The plan was similar to what they call now Pre Paid Cap Encore, which means you get $250 credit calls (which run out quick because of high minute tariff) and 500MB of data. You can see additional details here: http://www.telstra.com.au/mobile/prepaid/prepaid-offers/

Don't be tempted to buy the sim at the airport from Vodafone -- at the city they cost less.

I am using Woolworth mobile. It gives you $250 credit, another $250 credit for optus mobile only, 5G Data and 45 days expiry. You can check it by yourself. http://www.woolworthmobile.com.au