I'm surprised no one has mentioned the version sung by Jacqui McShee on the John Renbourn Group's "Enchanted Garden" album. I think it's the only time I've bothered to learn someone else's guitar part for a song.
John Peekstok

THE PLAINS OF WATERLOO

As I rode out one bright summer's morning,
Down by the gay banks of some clear and pleasant stream,
There I spied a fair maid making sad lamentations,
So I threw myself in ambush to hear her sad refrain.
Through the woods she marched along, caused the valleys to ring,
And the fine feathered songsters around her they flew.
Saying, "The wars they are over and peace it is restored again,
Yet my Willie's not returning from the plains of Waterloo."

Well I stepped up to this fair maid and said, "My young creature,
Oh, may I make so bold as to ask your true love's name?
For it's I have been in battle where the cannons round do rattle,
And by some strange fortune I might have known the same."
"Willie Smith's my true love's name, he's a hero of great fame,
And he's gone and he's left me and stole my heart, it's true,
Yet no one will I enjoy but my own darling boy,
Although he's not returned yet from the plains of Waterloo."

If Willie Smith's your true love's name, he's a hero of great fame,
He and I have been in battle through manys a long campaign.
Through Italy and Russia, through Germany and Prussia,
Oh, he was my me loyal comrade through France and through Spain.
Until at length by the French we were surrounded,
Like the heroes of old we did them subdue.
We did fight for three days until we did defeat him,
That bold Napoleon Boney on the plains of Waterloo.

On the eighteenth day of June was the end of the battle,
Leaving many a poor hero for to sigh and to moan.
Oh, the war drums they did beat and the cannons loudly rattle,
It was by a French soldier your Willie was slain.
And as I passed by where he lay a-bleeding,
Oh, I scarcely had time for to bid him adieu,
In a faltering voice these words he was repeating,
"Fare thee well, my lovely Annie, you are far from Waterloo."

Now when this fair maid heard his sad acclamation,
Well her two rosy cheeks turned to pale and to wan,
And when he saw this fair maid making sad lamentations,
Oh, he said, "My dearest Annie, I am that very one.
And here is the ring that was broken between us
In the midst of our danger to remind me of you."
And when she saw the token she fell into his arms then,
Saying, "You're welcome dearest Willie from the plains of Waterloo."