Greatest? Ever? I don't know about but I've been singing this one for over 40 years. It still makes me cry -

I Come And Stand At Every Door (also known as the Little Girl From Hiroshima) - Lyrics adapted from a Turkish Poem by Nazim Hikmet. Translated into English by Jeanette Turner. Adapted by Pete Seeger Music by James Waters,"The Great Silkie" (information courtesy of Where Have All The Flowers Gone? by Pete Seeger)


I come and stand at every door
But none can hear my silent tread
I knock and yet remain unseen
For I am dead -
For I am dead.

I'm only seven although I died
In Hiroshima, long ago
I'm seven now as I was then
When children die
They do not grow.

My hair was scorched by swirling flame
My eyes grew dim, my eyes grew blind
Death came and turned my bones to dust
And that was scattered by the wind.

I need no fruit, I need no rice
I need no sweets, nor even bread
I ask for nothing for myself
For I am dead
For I am dead.

All that I ask is that for peace
You fight today, you fight today
So that the children of this earth
May live and grow
And laugh and play.

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also in the cue (besides many already referenced by other posters):

God On Our Side - Bob Dylan
The Gentlement of Distinction - Malvina Reynolds
Political Science - Randy Newman
The Rainbow Race - Pete Seeger
The Merry Minuet - Sheldon Harnick
This World Is One - Charlie King

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In Peace and Song,
Joyce