Sound file: sopranos
Sound file: tenors
Sound file: altos
Sound file: basses
Here's what Wikipedia has to say about the song.
Although written almost 20 years earlier, by 1964 the song had already been recorded by several artists—including Frank Sinatra—but without much success. Lane was playing piano for Dean Martin on his Dream with Dean LP sessions, and with an hour or so of studio time left and one song short, Lane suggested that Martin take a run at his tune. Dean was agreeable, and the small combo of piano, guitar, drums, and bass performed a relatively quiet, laid-back version of the song. Almost immediately Martin re-recorded the song for his next album, this time with a full orchestra and chorus.
Although still a major recording artist, Dean Martin had not had a top 40 hit since 1958. With the British Invasion ruling the U.S. charts, few had hopes that an Italian crooner who had been singing mainly standards for almost 20 years would sway many teenagers. Martin resented rock n' roll, and his attitude created conflict at home with his 12-year-old son Dean Paul Martin, who like many young people at the time worshipped pop groups like The Beatles. He told his son, "I'm gonna knock your pallies off the charts," and on August 15, 1964 he did just that: "Everybody Loves Somebody" knocked The Beatles' "A Hard Day's Night" off the No. 1 slot on Billboard, going straight up to the top of both the Billboard Hot 100 and the Pop-Standard Singles chart, the latter for eight weeks.
It ultimately replaced "That's Amore" as Martin's signature song, and he sang it as the theme of his weekly television variety show from 1965 to 1974. The song has become so identified with Martin that later versions are invariably compared to his take.
"Everybody Loves Somebody Sometime" appears on Martin's grave marker in Los Angeles.