9. The Descent
One of British horror's best outputs since 28 Days Later, The Descent is the story of a group of female outdoors types getting trapped in an unknown cave system when out for a trip to rekindle their friendship, a year after protagonist Sarah lost her husband and daughter in a car accident.
Rife with mental as well as physical turmoil deep underground, the women discover that the caves have been left alone for a reason. Namely, there's a bunch of horrible pasty monsters out to eat anyone that stumbles through their territory.
With some genuinely disturbing sequences and a focus on an all-female cast, the emotional beats of the movie are almost as harrowing as their perilous situation. One jump scare in particular, that introduces the group's situation, is probably up there as one of the scariest unexpected moments in a movie - enough to bash the power button quicker than you can say 'now, that's enough of that.'