Bungie has announced that new Halo 3 map Cold Storage will be available on Xbox Live from Monday July 7th. And it won't cost a thing.
The same day, Microsoft is cutting 200 Microsoft Points off the price of the Legendary map pack - so it'll cost just 600 points (GBP 5.10 / EUR 7.20). However, you won't get the Bungie Pro Bonus (extra slots for uploading movies and pics to Bungie.net) for that price.
More details are available over on the Bungie website.