Microsoft promised games-on-demand for the Xbox 360 at last month's E3 show, and now it's ready to launch the service on August 11. The Xbox Live Fall Dashboard update will feature Games on Demand, a service that (at launch) will offer more than 30 downloadable Xbox 360 games, including Assassin's Creed, BioShock and Mass Effect. Microsoft plans to add additional games on an ongoing basis. Pricing hasn't been announced, so it's unclear whether the downloadable games will cost less than the boxed versions sold at brick-and-mortar retailers.

The August update also adds goodies for Xbox live users who subscribe to Netflix. These include improved video streaming and the ability to watched movies and TV shows simultaneously with other Xbox Live users, Microsoft says.

Lastly, a new Avatar Marketplace lets you outfit your digital alter ego with branded apparel from popular fashion labels and Xbox 306 games.

Conspicuous in its absence is the previously announced support for Facebook, Twitter, and Last.fm, which reportedly is scheduled for an Xbox Live update sometime this fall.