The most interesting feature in the upcoming Xbox Live update is the new "Games on Demand" service that allows you to download full Xbox 360 games to your hard drive. Today Microsoft announced the 21 games that will be available when the service goes live:

• Assassin's Creed (Ubisoft)
• Burnout Paradise (EA)
• Call of Duty® 2 (Activision)
• Elder Scrolls IV: Oblivion
• Fight Night Round 3 (EA)
• Kameo: Elements of Power (Microsoft Game Studios)
• LEGO Star Wars: The Complete Saga (LucasArts)
• Mass Effect (Microsoft Game Studios)
• Meet The Robinsons (Disney)
• MX vs. ATV Untamed (THQ)
• Need for Speed Carbon (EA)
• Need for Speed: Most Wanted (EA)
• Perfect Dark Zero (Microsoft Game Studios)
• Prey (2K Games)
• Rockstar Games Presents Table Tennis (Rockstar Games)
• Sega Rally (Sega)
• TEST DRIVE: UNLIMITED (Atari)
• Tom Clancy’s Rainbow Six Vegas
• Tomb Raider Legend (Eidos)
• Viva Piñata (Microsoft Game Studios)
• Viva Piñata 2: Trouble in Paradise (Microsoft Game Studios)

The Xbox Live update will also allow you to watch streaming movies with a group of friends and purchase premium clothing for your Xbox Live Avatar. It goes live on August 11th.

Update: Microsoft's PR informs us that the above list is the UK launch titles list. Here is the list of games that will be available through Games On Demand in the US on launch:

• Assassin's Creed (Ubisoft)
• BioShock (2K Games)
• Burnout Paradise (EA)
• Call of Duty® 2 (Activision)
• Dance Dance Revolution Universe (Konami)
• Fight Night Round 3 (EA)
• Kameo: Elements of Power (Microsoft Game Studios)
• Karaoke Revolution American Idol Encore (Konami)
• LEGO Star Wars: The Complete Saga (LucasArts)
• Mass Effect (Microsoft Game Studios)
• Meet The Robinsons (Disney)
• MX vs. ATV Untamed (THQ)
• Need for Speed Carbon (EA)
• Need for Speed: Most Wanted (EA)
• Perfect Dark Zero (Microsoft Game Studios)
• Prey (2K Games)
• Rainbow Six Vegas (Ubisoft)
• ridge racer 6 (Namco)
• Rockstar Games Presents Table Tennis (Rockstar Games)
• Sonic the Hedgehog (SEGA)
• TEST DRIVE: UNLIMITED (Atari)
• The Elder Scrolls IV: Oblivion (2K Games/Bethesda Softworks)
• Viva Piñata (Microsoft Game Studios)
• Viva Piñata 2: Trouble in Paradise (Microsoft Game Studios)