Tony Bennett sings his signature song, "I Left My Heart in San Francisco," finishing with Judy Garland in duet.
He first sang it in 1961 and has said this, "That song helped make me a world citizen. It allowed me to live, work and sing in any city on the globe. It changed my whole life."
For his 80th and 85th birthdays Bennett released "Duets" albums performing with a wide range of artists, from Paul McCartney and Elton John to Barbra Streisand and Michael Buble to Sting, Bono, and Gaga.
The song was written by Douglas Cross and George Cory. While it is not technically a showtune (that I know of), it ought to be!