Taxi Driver (1976)
Martin Scorsese details the life of a New York City taxi driver who is struggling after the war. His PTSD triggers some halluncations and bouts of rage, but we're always left wondering what's real and what isn't. Robert De Niro absolutely nails this role.
The Exorcist (1973)
Known as one of the scariest films of all time, The Exorcist completely remade what horror movies meant to society. The special FX of the time was brand new to the audience which apparently terrified them even more. This film became even more famous down the road due to the bizarre and creepy things that happened to cast members during and after filming.