The recent death of Ken Russell just made us appreciate Altered States even more. This is a mind horror movie as much as a body horror one - the story of a university professor who experiments with psychoactive drugs and sensory deprivation only to find himself regressing to a more primitive form of life is a little artsier than some of the other flicks on this list, but no less nerve-wracking. When our protagonist basically becomes an undistinguished blob of protoplasm, you will feel a little sick to your stomach, but that's what makes this one of the best body horror movies now isn't it?