My personal favorite has to go to Alien-" in space no one can hear you scream" it's a chilling phrase, and the movie absolutely delivers on what the tagline provides. Zodiac is also one I really like "there's more then one way to lose your life to a killer"
Another thing I also noticed is that both 2011 Drive and 2007 No country for Old men have the same tag line- "there are no clean getaways" funny little similarity that I noticed in the posters.