A few Nordic contributions:

Byssan lull: https://youtu.be/ogYC4LgqqnM A lullaby I think all Norwegian children have heard their beds, but it's actually Swedish

Til ungdommen: https://youtu.be/CieUTG8Z6Z0 The song became very beloved after 22.07.2011 and I think close to everyone here will get tears in their eyes when they hear it

Mitt hjerte alltid vanker: https://youtu.be/27JqZ8eEZlw Since it's Christmas soon. Very popular in Norway, although it's originally Danish

I guess it demonstrates the close historical relationship between the Nordic countries