The 3rd map pack for Call of Duty: Black Ops was leaked, but it's only a rumor so far. This image shows the content of the new map pack for Black Ops, included are 5 new maps :
New Zombie level
Although this is only a rumor, it could be possible. The second map pack, The Escalation pack, was also leaked (which you can see here) about a week before its official announcement by retailer GAME via a promotional advertisement. The new image above comes most likely from a GameStop due to the text "Downloadable Content is better at GameStop" on the ad.
Call of Duty: Modern Warfare 3:
The Beta start July 14, if you're interested you must own Black Ops. Over two million players have already signed up for it.