"Summertime," by Ella Fitzgerald

"Summertime," Ella Fitzgerald Ella's version of "Summertime," technically a cover of George Gershwin's aria composed for the 1935 opera Porgy and Bess, is still utterly jaw-dropping. Gershwin's mix of jazz elements and African-American folk music worked so seamlessly that it would be hard to ignore the song's validity as a jazz standard even if Fitzgerald had never touched the tune. But she did, and did so in a way that really can't be outdone.
http://www.houstonpress.com/music/the-10-most-quintessential-old-jazz-songs-6529372