<img src="https://beta.techcrunch.com/wp-content/uploads/2007/01/GameStop just got in on the pre-order action with their own "GameStop Universal Premium HDMI Cable". There may not be an official announcement from Microsoft saying whether they support HDMI, but unofficially, there are at least two manufacturers who've jumped the gun.
Whether the Xbox 360 will need the HDMI cable to display HD DVD content is unknown, but unlikely. Component has been doing a fine job already with HD gaming, so if it's required, it's only for the movie studio's sake. The ship date is listed as 12/1 and the price is $99.99.
GameStop Universal Premium HDMI Cable [EBGames]