I discovered Estrellita, by Manuel Ponce, through Heifetz's famous arrangement of it for violin and piano:  

 

Even though the melody is perfectly suited to a violin, the piece is originally a song. Here are the lyrics, their English translation, and a recording:  

Estrellita del lejano cielo, 
que miras mi dolor, 
que sabes mi sufrir, 
baja y di me si me quiere un poco 
porque yo no puedo sin su amor vivir.

Tú eres estrella, mi faro de amor, 
tú sabes que pronto he de morir. 
Baja y di me si me quiere un poco 
porque yo no puedo sin su amor vivir.  

Little star of the distant sky, 
you see my pain, 
you know my anguish. 
Come down and tell me if he loves me a little, 
because I cannot live without his love.

You are my star, my beacon of love! 
You know that soon I shall die. 
Come down and tell me if he loves me a little, 
because I cannot live without his love.

 

What's so remarkable about this song is the contrast between the sweetness of the melody, and the sadness of the lyrics. Of course, that's why it works so beautifully.