It all began with, well, It

• It was the title of an Ernest Hemingway novel in 1970.
• The Bee Gees wrote it.
• Kenny Rogers and Dolly Parton scored a massive hit with it.
• Kikki Danielsson covered it in Swedish.
• Tomeu Penya added it to dialect of the Catalan language.
• Starbucks had a compliation of The Constantines featuring it.
• Barry Manilow rode on its coattails.
• More recently, Carrie Underwood paid tribute with it.
• American Idol Season 4 saw the contestants revving it up.
• Comic Relief 2009 covered it and entered the UK charts at Number One. (Wow!)

What is It?
Islands In The Stream, of course!
On that note (pun unintended), the chorus is particularly charming.

Islands in the stream
That is what we are
No one in between
How can we be wrong

Sail away with me
To another world
And we rely on each other