Well I am currently working on a mod that adds places. But it is nowhere near done. (I will need beta testers) However might I direct you too another mod. It is called http://www.fallout3nexus.com/downloads/file.php?id=11018. It too is a WIP but its very near complition. So if you want something thats 100% done ignore this.
Also there are so few mods that add places to the game that are well made and completed... Thats why the mod I am making (see signature) is hopefully only the first in a series of mods that add new places to the wastes. I will also probably immidiatly start making mods like this for NV when it is released. (Provided it is mod-able like FO and TES) I hope to be the number one guy when it comes to mods that add Dungeons/quests/places to the game.