Figured I'd chip in my two cents as a United Statesian who has traveled a good portion of the world...
Vegas and Hawaii are fun, if you've got cash to spare... the eastern seaboard megalopolis is something I prefer to avoid, though. Dickheads per capita seems to go up the further you get into the the crowded areas there.
Most of what the US has to offer that you won't find many other places in the world lies in our nature reserves and such, though. Yellowstone is a good example, but it's one in thousands.