"The Universal Soldier" by Buffy Sainte-Marie
"Handsome Johnny" by Richie Havens and Lou Gossett
"Saigon Bride" by Nina Duscheck and Joan Baez
"The Fiddle and the Drum" by Joni Mitchell

The original poster mentioned pro-Vietnam war songs as well, so here goes:

Hello Vietnam
(Tom T. Hall)

America has heard the bugle call,
And you know it involves us one and all.
I don't suppose that war will ever end;
There's fighting that will break us up again.

Chorus:
Goodbye my darling, hello Vietnam;
A hill to take, a battle to be won.
Kiss me goodbye and write me while I'm gone.
Goodbye my sweetheart, hello Vietnam.

A ship is waiting for us at the dock.
America has trouble to be stopped.
We must save freedom in that foreign land,
Or freedom will start slipping through our hands.

(Chorus)

I hope and pray someday the world will learn
That fires we don't put out will bigger burn.
We must save freedom now at any cost,
Or someday our own freedom will be lost.)