EDIT The price is now $199.(25th DEC) EDIT 2…The offer is back. (26th DEC)
EDIT 3…Out of stock (27th DEC)
I think this one trumps all the others guys.
grababargain's comment got me curious whether the Microsoft store is included in the promotion.
Ringing up, I found out that it does qualify, so long as I purchase between the promotional period.
Currently there's also an offer for 2 FREE games, although the rep couldn't guarantee if it would still be available on the 26th. Although I would assume it would, as the fineprint states: "Offer valid from 15 November 2013 until 14 January 2014, while supplies last."
EDIT: You have to print out the emailed receipt from the Microsoft store as well as the page(s) from xbox360cashback.com.au and mail it to them no later than the 31st of January.
The cash back will be deposited into your selected bank account in 8-12 weeks.