SIMPLE30
From FB post:
"Hey Facebook friends.
We are giving 30% off our online store for only a couple of days.
Use the code - SIMPLE30 at the checkout to receive the discounts.
www.mrsimple.com.au/collections/all"
Not too sure when it expires but just worked for me. They've also got free shipping on all orders.
I was also given a code for 10% off my next purchase in the next two weeks as well as a code for $20 off on purchases over $75 in the next 30 days.