Chinatown. Greatest screenplay, just a masterpiece. All The Presidents Men, The Conversation, Apocalypse Now, Walkabout, Dog Day Afternoon, Badlands, Mean Streets (alright I know Walkabout is a bit more arty, but hey)... also that strain of sci-fi that produced Rollerball, Silent Running..
Man Dog Day Afternoon. What a great film that was and based on a true story too. ATTTICCAA!