Quantas will begin offering service from SFO to Sydney beginning later this year. However, it seems this will be on a 747-400ER rather than a newer widebody like the A380 that Quantas operates on other long-haul routes.
American will also being service to Sydney from LAX starting in December 2015. Unlike Quantas, this one will be flying a 777-300ER but will have fewer First/Business class seats.
Since both of these are One World alliance airlines, that now means two more ways to get to Australia from the US.
Read more about the two airlines in this article.