This morning saw the announcement of Fallout: New Vegas.
Though it's not a sequel to Fallout 3, it is set in the same universe and is being developed by Obsidian Entertainment — a development house chock full of people who worked on the first two Fallout games.
As the title implies, the game takes place in post-apocalyptic Las Vegas.
And that's the extent of what we know.
While I applaud the change of scenery, I would like to point out that — despite what the above picture might imply — legalizing Radscorpion prostitution is a terrible idea. You just don't know where those things have been.