New York (city.) Although I'd be utterly sick of it...
Tokyo (if not a place in America.)
Las Vegas (for the mass murder kind of thing.)
Atlantic City (Another mass murder tactic.)
I think that the most fun would be in- you guessed it- DISNEY WORLD! I would love to see Orlando in ruins with a big ol' mickey mouse statue with half its head blown off, you know, the tea cups got corpses in it and the giant epcot globe has been turned into an Enclave hide out... Ah, good stuff. Cinderella castle + brother hood of steal any one? Lol. But of course that would just be that part of the place, the rest of Orlando would be wastelands.
PS. London sounds really good, Paris even.