Although not every currency is up and running at time of writing, Blizzard has opened the doors on the Diablo 3 Auction House.
You will now be able to fork out actual US, Australian, and Mexican cash, not just in-game currency, for virtual items. Expect European and other American currencies to go live "in the near future".
Trading is limited to equipment right now, with commodities - presumably crafting supplies - to be introduced at a later date, hopefully after Blizzard figures out how to stop people with economics degrees miniting it off the rest of us.
Blizzard has asked players to be patient as trading may take some time to process during the service's initial launch.
This is probably going to be one of the most interesting digital monetisation experiments of this generation so sit back and watch the fireworks - and feel free to shill your best listings in the comments thread. I really need a good double resist pauldron, just FYI.