Not really a duet so much as two sides of a short song, but "All I Ever Wanted/Queen's Reprise" from THE PRINCE OF EGYPT.
"The Letter" from BILLY ELLIOT? So long as we're accepting Ghost Mothers... also Funmilayo's songs from FELA! but I doubt those are what we're looking for.
Words don't deserve that kind of malarkey. They're innocent, neutral, precise, standing for this, describing that, meaning the other, so if you look after them you can build bridges across incomprehension and chaos. But when they get their corners knocked off, they're no good anymore…I don't think writers are sacred, but words are. They deserve respect. If you get the right ones in the right order, you can nudge the world a little.