So the HD DVD format is officially dead, that's old news. Unfortunately, there are companies out there still producing players for this now defunct format, including Microsoft. Don't expect to see those HD DVD player add-ons for your Xbox 360 on store shelves much longer though.
Microsoft has officially announced that they will no longer be offering the HD DVD player accessory for your 360. It really comes as no surprise to hear, since everyone else is calling it quits too.
There is a silver lining to this story. If you're looking for a cheap upscaling DVD player, you can almost bet that these will be clearanced off for next to nothing, so keep your eyes peeled.