These are perfect screenplays... which are not to be confused with perfect movies. There are others but these are what comes to mind.
  1. Butch Cassidy and the Sundance Kid
  2. The Truman show
  3. Stay
  4. American Pie
  5. Body Heat
  6. American Beauty
  7. Reservoir Dogs
  8. The Apartment
  9. Crimes & Misdemeanors