The Fog (1980): This tale of woe visited upon the Northern California town of Antonio Bay because of the ignoble actions of their ancestors is chilling indeed. The brilliant timing of the movie, the sense of disquieting dread, and the remorseless approach of evil makes it a must watch film. Just a note: Don't confuse this outstanding film with the execrable 2005 remake which was so bad that every existing copy should be buried at the bottom of the Marianas Trench.
The Mist (2007): A sinister story about a deadly government experiment and how quickly human beings can become primitive again when they're isolated, alone, and in danger. Oh yeah, there are also weird monsters, a menacing mist, and a well-written Stephen King plotline. The ending is, ah -- let's just say, you don't want to know how it ends until you see it.
Quarantine (2008): When zombies infected with super-rabies are trying to kill you and the government shows up, count on them to stand outside, picking their noses and trying to figure out what to do, while you struggle for survival. It's a timely and true message: Don't count on your government in a crisis. Also, don't get trapped in a building with zombies. We shouldn't forget that either.
Re-Animator (1985): This movie is little funny, a little macabre, and a little gory. Somewhere in there is also a message about the perils of playing God with human life. That's a message that's all too timely given some of the morality free experiments scientists across the world are working on.
The Silence of the Lambs (1991): Fundamentally decent FBI agents match wits with one of the great horror villains of all-time, Hannibal Lecter, in an attempt to stop a serial killer. This isn't as pure a horror flick as some of the other films on the list, but it will keep you riveted to the screen.
The Tripper (2007): This movie is meant to be a slap at Ronald Reagan and conservatives. In a couple of spots near the end of the movie, it does manage to grate conservative sensibilities. However, that mild annoyance does not to detract from the sweet, sweet joy of watching a guy in a Ronald Reagan mask taking an ax to dirty, drug addled hippies throughout the movie. If a conservative had made this movie, instead of David Arquette, liberals would be calling it a "hate crime."