The latest Diablo III patch has been deployed which most notably brings the real money auction house online. At the current time, the auction house is only available on the Americas servers with the EU auction house to be added at a later date.
To access the real-money auction house, click on the "Auction House" button on the left-hand side of the campaign screen, and then on the button showing your region's currency in the upper right-hand corner of the auction house interface. This will switch you between the gold- and real-money auction houses. Latin American players will have access to trade using the United States dollar, Australia dollar and Mexican peso.
Read the full blog post on the Diablo III site.