2001 and The Big Lebowski take my top two spots easily. The Shining is usually also a top-5 staple, as is Apocalypse Now. After that it gets tricky, 50 candidates for one spot. Among them The Maltese Falcon, Sorcerer, Fail Safe, Anatomy for a Murder, 12 Angry Men, Rear Window, The French Connection, Ed Wood, The Seven Samurai, etc. etc. etc.