Some of the major bullet points include:
HD 1080p video mode support over VGA and component cables.
Xbox 360™ HD DVD Player support.
Stream WMV video from a Windows PC running Windows Media Player 11, Zune software, or Windows Media Connect.
Play video from storage devices such as USB flash drives, Xbox 360 Memory Units, etc.
Play video from CD or DVD data discs.
Xbox 360 Wireless Headset support, including battery level indicator in the Xbox Guide.
Video support for 50 Hz HDTV modes (DVD and HD DVD only).
Xbox 360 Wireless Racing Wheel support.
Set up automatic downloads of newly released Xbox Live Arcade trial games.
Support for upcoming release of XNA Game Studio Express (separate download and subscription required.)
Stream music, pictures and video from a Zune device.