This one flew in waaay under the radar, but high-quality genre homevid purveyor Dark Sky Films has partnered with Microsoft to release several titles from their impressive catalog as HD downloads via the Xbox Live Marketplace, a function of the Xbox360's online capabilities. There's very little information out there right now, other than some titles having been confirmed as available for rental / purchase, including 720p versions of The Texas Chainsaw Massacre and Eaten Alive.
Anchor Bay has thrown their hat in with Blu-Ray; Dark Sky has partnered with the HD-DVD-friendly folks at Microsoft. Even though the lose/lose format war rages on, it's encouraging that smaller companies are entering the HD fray.