Some good films already mentioned. May I add a film titled "Fail Safe"? It was about a B58 crew who, due to a computer error, received the authentication codes to go and turn Moscow into dust. As a gesture to the Russians , the US president (played very well by Henry Fonda), turned New York into an open space. It was a very sobering and thought provoking film.
The worst film?.....got to be Pearl Harbour.