Lebara Mobile: Prepaid Sim with special low cost international rates
Sim is free, then international calls from 5c a min depending on the country.
You also get $15 free when you recharge $30. You also get $5 free when you activate online.
Definitely a good deal for those who want to make international calls from their mobile - when I was in the UK and phoning Australia a lot, I had one of these type of sims!