The Man Who Shot Liberty Valance
(A little trivia- Lee Marvin got his name from a distant cousin - R. E. Lee which makes him a distant cousin of Bob Duvall)
Fort Apache
The Quiet Man
As well as the Duke, I really like his old friend Ward Bond. Bond hold the distinction of appearing in more AFI top 100 films than any other actor.
In his great bio of Coach Bryant, Allen Barra made the comment that once Coach died, thousands of Alabamians would no longer know what it was like to have John Wayne a grandpa. Or something to that effect.
I always loved Stagecoach, Sons of KE and the Longest Day.