United has some awesome fares to Sydney and Australia right now from selected cities including Atlanta, Salt Lake City, Detroit and Seattle.
The flights usually go via Denver and Los Angeles and then on the new 787 to Australia. Note that teh fare has a two week (!) minimum stay.
This G fare should earn 100% on Singapore Airlines Krisflyer.
They are available in our flight search for $495 RT and can be booked directly on United.
You can travel even cheaper if you combine two one-ways and return to Los Angeles and fly from Salt Lake City which would be a good option for West Coast flyers.
Thy this Google Flights link to see prices as low as $404 for this Open Jaw RT.