As was outlined during their E3 press conference, Microsoft will be adding a digital distribution service to Xbox Live as part of a planned August 11 dashboard update.
The digital distribution service, dubbed Games On Demand, will launch with some key titles, including the likes of Mass Effect, Assassin's Creed and BioShock. The initial manifest is 30 titles long, but Microsoft are promising more and more games will be added once the service is up and running. We've contacted Microsoft Australia to find out if this update will apply locally, so stay tuned for a response.
Check out Gamasutra
for a more detailed run down.