Schubert - Ständchen (superbly sung by Peter Schreier, with Rudolf Buchbinder at the piano) 

https://www.youtube.com/watch?v=oaq-6U7ZJt8

(I must really try to restrain myself now, as if I start posting Schubert's Lieder I won't be able to stop...)

I will only post one more...

Schubert - "Gute Nacht"/"Good Night" from "Winterreise"/"WInter Journey" (sung by Peter Schreier)

https://www.youtube.com/watch?v=tZb6a6wr_60

This is long, but wow, so beautiful! Absolutely divine.

Maria Callas - 50 Most Beautiful Opera Arias

https://www.youtube.com/watch?v=1iwGIBewHPM

Because many of us love stars and the night sky...

E Lucevan le Stelle (from Puccini's Tosca, sung by Luciano Pavarotti)

https://www.youtube.com/watch?v=UuQdEyz6b6w

That same aria… E lucevan le stelle sung by Franco Corelli… It ‘s beyond perfection.

https://youtu.be/vw6L0jFseUI

And by Jonas Kaufmann: https://youtu.be/S-8ulgLFEl4

And… Plácido Domingo: https://youtu.be/5-AF1T4OehM

The glorious Pearl Fishers Duet (Au fond du temple), sung by Jonas Kaufmann and Dmitri Hvorostovsky, in one of the finest performances imaginable.

https://youtu.be/p2MwnHpLV48

Mussorgsky - Pictures at an exhibition

https://youtu.be/UBuSJXObgpw

This live version is conducted by Solti. You might have to turn up the sound a little, but this performance is outstanding.

Monteverdi - Ohimé, dov'il mio ben, sung by Claron McFadden and Nora Fischer, with Mike Fentrs on the theorbo.

https://youtu.be/GH0PLm6Q8V4

For a more Italian approach and pronunciation, the performance below is by Roberta Invernizzi & Gloria Banditelli.

https://www.youtube.com/watch?v=nvmyADhtqfk

And for the first version I ever heard, which remains radiant even in the sorrow of the words, agile and full of delicious vocal turns... Emma Kirkby and Evelyn Tubb, accompanied by Kirkby's husband, Anthony Rooley on lute (or possibly on theorbo).

https://www.youtube.com/watch?v=v4voBLxGxWI

Mozart - Eine Kleine Nachtmusik (I. Allegro)

https://www.youtube.com/watch?v=oy2zDJPIgwc