Some of my favorites that aren't well-known, particularly by younger audiences:
"Being There" (Peter Sellers)
"Switchback" (Dennis Quaid)
"Fail Safe" (Henry Fonda)
"The Idolmaker" (Ray Sharkey)
and two with football angles to them:
"Everybody's All American" (Dennis Quaid). Screenplay by SI writer Frank Deford has a brief sequence when Quaid's character joins the Denver Broncos and is spliced into scenes of that great 1978 win over New England in the snow at Mile High.
"The Fortune Cookie" (Jack Lemmon). Walter Matthau steals the show as a scheming tort lawyer brother-in-law but there are scenes of Lemmon on the sidelines of a Cleveland Browns game with a young Keith Jackson playing the tv announcer.