It's called the Escalation Pack. The next Map Pack that will include 5 new maps to Call of Duty: Black Ops Multiplayer. An Australian retailer GAME supposedly leaked an add about the new Map Pack . They pulled the ad out but it's too late now, the info is out.
Of course it will arrive on Xbox 360 first because of their 3 year exclusive deal with Activision. It said to arrive on the Xbox on May 3. PS3 and PC is of course not yet announced and will be probably released a month after the Xbox release.
The Map Pack will include four multiplayer maps and one new zombie map just like before and will probably around $14.99.
Will update when there is official word from Activision but for now see the ad for yourself below.