The Zune HD is out today. Doesn't yet have much to do with the 360, aside from these Zunes engraved with logos and characters from current and upcoming 360 games.
They're part of the Zune's "Xbox Series". Which basically means you buy a Zune, then pick from one of ten designs (pictured below) that can be officially engraved on the back of your player.
Note: the one above is a mockup, since being in Australia the Zune store won't even let me access actual pictures, let alone buy one.
Xbox Series [Zune]