9. "Nightmare At 20,000 Feet"
We don't care how low-budget that ambiguous creature on the airplane wing looks; our guess: some helpless PA was shoved into a yeti costume with an afro wig plopped on his head. This episode is, hands down, one of the most nerve-racking of the series, and anyone who claims they didn't leap away from the TV the first time William Shatner flipped up the curtain and finally sees the monster is a liar. Unfortunately for Captain Kirk, no one believes his claim that something is outside tampering with the plane until after he's forced to take matters into his own hands. And you thought Delta's in-flight movie selection was scary.