Halo 3: ODST was released last night. It retails for $99.95, but you can get it for a bit cheaper than that right now. Or, if you wait until Thursday, you can get it for much cheaper at Big W.
$68, to be exact.
Or you can get it for free when you buy the Elite console bundle for $398. And get Call of Duty: World at War throw in too.
Big W Catalogue Until September 30th [Ecogamer]