The "He Walked Up The Hill" public domain protest folk song was written in 1968 after MLK's assassination and a video of this song was recently posted at following youtube link:
http://www.youtube.com/watch?v=PG7NGJWxqAc

"He Walked Up The Hill" (for Martin Luther King)

He walked up the hill
And he knew that it was willed
That the white racists they would slay
All the good men who crossed their way
And what else is their left to say
Look! The Black Prince of Peace now lays.

And all go and pray
Though they kill people everyday
Their soldiers kill 'cross the sea
Their cops shoot up the cities
Their managers steal our bread
Their teachers, they ruin our heads.

"Be NON-VIOLENT!" they scream
For they fear what we all will dream
Now that Moses is dead
Shot in the back of the head
"Love them" is what he said
Yet look how they treated him.

The hearts now are red
As they rise up from their beds
To say to the Man with hate
"We're sorry but it's now too late
We want to control our fate
The Panther will kill your snake."

Also, Rev. Frederick Doublass Kirkpatrick's Ballads of Black America album from Folkways of 1972 includes Kirk's biographical folk song about Martin Luther King, "Ballad of Dr. King."

"Ballad of Dr. King" (by Rev. F.D. Kirkpatrick)

There was a man from Atlanta town
From a mountain top he had a plan
He marched with God

In a Birmingham jail
Down on his knees
He had a date and he conquered hate
And he marched with God.

A man he said in spite of it all
Is nothin' but a man And he must not fall
A woman too said Rosa Parks
On Dusty roads
In courthouse squares
Wherever he went
Love was always there

The dream that he had was full of peace
It burned his soul
He cannot cease and He marched with God

In brotherly love
He marched with us all from Alabama
To Chicago and New York
In brotherly love
He marched for us for us all
Until that day he met his fall.

To hear a clip from Kirk's folk song, you can click on following link:
http://www.folkways.si.edu/TrackDetails.aspx?itemid=17163