Qantas is running Los Angeles to Sydney for $160 plus all taxes, which omes out to about $500 – $520 all-in. It’s valid for November and December travel on their new Airbus A380 and you need to depart on Monday or Wednesday (many more Wednesday departures are actually available) and return on a Wednesday, Friday, or Sunday.
Best to try flexible date search using the Qantas website or booking engine with similar functionality such as Travelocity, since it can be somewhat tricky to find availability.
This is the lowest I’ve ever seen US to Australia. The flight won’t even credit full 100% mileage in American’s frequent flyer program, but if you credit the points to Qantas or LAN you’ll receive full mileage.
The Flyertalk discussion is here.
Update 1:20pm Eastern: The fare no longer appears to be available.