Rezurrection releases tomorrow (Tuesday, Aug 23rd) for those that haven't been up to date with the news on Live. It comes with the 4 original zombies maps from World at War, as well as a new map: Moon.
The pack also includes a download of the Call of Duty: Zombies soundtracks. If you already have the map pack by pre-ordering the hardened or prestige edition, then you already get the extra content. FREE. Simply re-download the map pack.
For those that don't have it already, it will set you back a hefty 1200MS points, but if you're a zombies person, This map pack is for you.