Currently there are two HD DVD formats in development: HD-DVD by Toshiba and NEC, and Blu-Ray developed by Sony. The two formats are not compatible with each other, so in order to play a Blu-Ray HD movie, you will need a Blu-Ray player (not a HD-DVD Player).
BestPrices.com will list all the available Blu-Ray HD DVDs here on this page as soon as they become available. Check back for more news on this new format!