Amaysim is currently doing a 50% off promo on their unlimited plan, first month only. Usually $39.90 and with code 50UNL UNL50 it would be $19.95 for the first month.
The conditions of the promo are:
- Offer only available to new customers who buy their SIM Card online using credit or debit card
- Discount only applies to a customer’s first month of Unlimited
- Offer expires on 28 July
Edit: Btw Qwibble is doing $39 cashback on the Amaysim unlimited plan. However you usually need to be on the plan for 3 months before Amaysim will release the commission to Qwibble (which then gets rebated to you). So you can't really make a profit here ($39 > $19.95).
Amaysim doesnt have the advantage now that boost is with Telstra (only 10c more a month), only thing is you get 1GB less. Vaya is $45 unlimited (but you get 4G LTE).