one I use regularly on wedding videos which usually have a slide show sequence (eg a la Nero) is
Salur d'Amour (Elgar) it was a love song to his wife (discuss).
the advantage is that without words people can comment - and they will.
The length is about right but if you do more slides than I would - consider Chanson de Matin (Elgar) it has the same feel. They were, in effect, Elgar's first hits. He sold them for about �100 which was a fair amount of money.