Bungie has the scoop on its Heroic Map Pack for Halo 3, which costs 800 Microsoft Points (or $10 for you mere mortals):

It’s that time again. DLC for Halo! Halo 3’s first ever downloadable content will be the Heroic Map Pack – a trio of amazing new maps, each with a completely different purpose – and each brand new to the Halo universe. No remakes (yet)! They’re going to be available about 2am PST on Tuesday, December 11th and you should all be waiting up to play them (except for the lucky few who grabbed the maps when they accidentally went up early on Monday).

The Halo 3 Heroic map pack is a collection of three new maps for Halo 3. Rat’s Nest, Standoff and Foundry – each providing a unique Halo 3 multiplayer experience.

A couple of important points: These maps will be free next year. And you need an Xbox Live account to download them now.