Activision detailed the DLC in a press release. The bad news: it's actually called "Rezurrection." The good news: it's launching August 23 on Xbox Live, and includes three "re-mastered levels of Zombie lore: Nacht der Untoten, Verruckt, Shi No Numa and Der Riese, the Zombie factory that started it all," along with a brand new "Moon" level. It also includes an "enhanced Zombies Soundtrack" and a new Zombies Moon theme. Yes, by the way, this is really about fighting zombies on the moon.
The four "remastered" maps were previously included with the Hardened and Prestige releases -- if you already have one of those, the rest of this content will be free. Otherwise, it's the standard 1200 MS Points/$15. It'll be easy to acquire, too, according to One of Swords: " the short version is you'll be able to go into your Download History and re-download the classic pack you already own, and the fresh download will include the new Moon map. And you'll also get the soundtrack and theme, too."