The subject of my post says it all, I think, or almost

I am indeed looking for some of the most poignant and heart-rending lieder, arias, duets, etc, (vocal works only, though). Being a pianist, I'm afraid I'm not as knowledgeable when it comes to vocal repertoire as I'd like to be.
I've already got a little few such as Donizetti's 'Il dolce suono', Mahler's 'In diesem Wetter' from his Kindertotenlieder and Händel's 'Lascia ch'io pianga'. Any other suggestions would be
much appreciated!
Cheers!