Which Frank Sinatra albums from the 1960s are considered major works?

During the 1960s, Frank Sinatra recorded at a prolific pace after founding Reprise Records in 1960. While some of his output during this period was of uneven quality due to the sheer volume of recordings, two albums from the decade are widely considered masterpieces on par with his finest work from the 1950s:1

• September of My Years (1965): An acclaimed album arranged by Gordon Jenkins.1
• Francis Albert Sinatra & Antonio Carlos Jobim (1967): A celebrated collaboration with the Brazilian songwriter Antônio Carlos Jobim.1

Although Sinatra achieved significant commercial success during the 1960s with hit singles such as "Strangers in the Night," "That’s Life," and "My Way," his later work in the decade was sometimes hindered by attempts to appeal to the youth market or inconsistent choices in collaborators.1