In addition to his absolutely awesome singing skills, Sinatra was a decent actor as well. Consider his stretch of wonderful performances in the mid to late 50's:

"From Here to Eternity" - as Maggio, he won the Best Supporting Actor in 1953, in a much deserved role (the basis for the Johnny Fontaine story in "The Godfather").

A few musicals with some wonderful songs - 1954's "Young at Heart" and 1955's "Guys and Dolls". My favorite musical with him was his portryal of Joe E. Lewis in "The Joker is Wild", the true story of an up and coming singer who crossed the Mob and nearly died because of it.

Great dramatic roles - as Don Cardi mentioned, "The Man With the Golden Arm", in which he portrayed a drug addict, and my favorite, "Some Came Running" in which he portrays a gambling man who teams with Dean Martin.

The lighter side of romance and family ends the decade with his touching portrayal of a dad in financial straits in "A Hole in the Head".