Best Trailer of my Generation (Horror): Alien.

Everybody now knows the premise of the movie, but back then we knew zip. And the beauty of the trailer is that it told you nothing. No words, just faces with fear including a cat. We were riding the wave of SciFi movies (Star Wars et all) and you were wondering what the heck this movie was about.
And then the tag line screwed with your mind. Your last act of defiance which is scream for your life, in anger, in fear is for naught. Horror Zen anyone?