It's called a Keep Cup.
They are a part of the green office initiative, and they are so good. The idea is that you bring this cup around with you, made of a strange material called polypropylene, and give it to the barista at a coffee shop every time you go. It is made in standard sizes that are used in Australia, so their money making is not scutinised, and it saves the need to squander coffee cups all round.
I got mine for free, but they usually cost 12 dollars.