Paul Simon and Art Garfunkel included the old English ballad, Scarborough Fair, on their immensely popular 1965 album, Simon & Garfunkel. I have always loved this melody set in Dorian mode and over the years have enjoyed the multiple possibilities it lends for harmonization and arranging. Here they are, singing it for a huge crowd in Central Park with the simplicity of solo guitar and their lovely vocal harmonies.
The version on their 1965 album featured the antiwar song, Canticle, as a countermelody, heard here:
And finally a more elaborate version that includes piano!