Okay had some thoughts on DLC for Fallout New Vegas and here is what I had in mind
first having the Alamo as a quest you could find gear like Davy Crockett's musket, or Jim Bowie's kinife. you could even have a last stand event against ghouls or some other creature.
Then you could have Roswell or Area 51 for the alien aspect of New Vegas .
and then last probably have Yellow Stone national park as a pitt spinoff.
Just brainstorming