If I were to travel to the US I would try and make it to Kitts Peak
http://www.noao.edu/kpno/
and if I were in the Chicago area:
http://www.adlerplanetarium.org/
and if I were in Hawaii I'd make sure to visit
http://www.ifa.hawaii.edu/mko/
Also its worth checking the US Sky and Telescope or Astronomy and there may be a star party happening somewhere close to where you are going to be..
Its really sad I' ve been to the US about 25 times and never managed a visit to any really interesting place -other than the National AeroSpace (Smithsonian) in Washington DC which is really a great day out as someone has already pointed out above.