Halo: Reach's upcoming map pack will be called "Defiant Map Pack" according to a French Halo fansite HaloDestiny. The DLC pack will reportedly include three maps: "Condemned," " Training Preserve" and "Unearthed." Microsoft has not confirmed any of these details. A Microsoft spokesman released the following statement, "We can confirm there will be additional downloadable content for “Halo: Reach” in the future, however we have nothing to announce at this time." HaloDestiny has since gone offline by request of Microsoft and Bungie.
HaloDestiny may no longer be online but HaloReachForum.eu still is. According to them Condemned will be 4-8-12 player map, Training Preserve will be a 8-12-16 player map and Unearthed will be a map for Firefight. A Flickr site is currently hosting all the screenshots of the maps from the original HaloDestiny post. All of this information is speculative. G4 will keep you posted as more details become available.
What do you want to see in future Halo: Reach DLC?