I just found out today that the leak we all heard about last week from GAME site is true. Of course, the flyer announcing this has since been removed. Activision and Microsoft will be dropping the $15.00 expansion pack May 3 for 360, PS3 and PC. This is the best kind of accidental leak ever. Below is the flyer that "accidentally" popped up on the site.
From here it looks like the new maps are as follows: Zoo, Hotel, Convoy, Stockpile, Co-op Zombie Mode.
Thank you GAME. I knew I loved Australians for some reason.