Halo 3 Heroic Map Pack (new maps)

It was just announced that three new Halo 3 maps will be released in December. The Heroic Map Pack will contain Standoff, Rat's Nest and Foundry. The map pack will be available for 800 points (then free in Spring of '08) beginning Tuesday December 11th. 

Details at Xbox.com

Edit: Bungie has more details (and screen shots) here