I love making lists! My top 10 are:
Godfather I
Godfather II
Sunset Boulevard
Stalag 17
Dog Day Afternoon
Fargo
Zorba the Greek
Amarcord
To Kill a Mockingbird
Witness for the Prosecution
Some that may not be "great cinema," but are lots of fun to watch:
The Discreet Charm of the Bourgeoisie
Two for the Road
Steel Magnolias
M.A.S.H.
Goodfellas
Shoot the Piano Player
Tom Jones