Most achingly-beautiful music

What, no Vincent LaGuardia Gambini?

Great question -- so many beautiful and truly moving songs, it's difficult to pick just 3. Fortunately, many of the great ones have already been mentioned above. Here are 3 more that always make me feel there is something more to life than our physical existence: (1) "Psalm" by the Jan Garbareck Group and Agnes Buen Garnas (on Twelve Moons), (2) Oregon's "Icarus" (Live), (3) the Jai Uttal/Lakshmi Shankar/Don Cherry rendition of "Raghupati" (on Footprints).

They all kill me.

The Mozart piece that was used in the British Airways commercials (don't know the name of it).

Dekay, a piece frequently referenced from the British Airways commercials is the Aria from the opera "Lakme" by Delibes. Not sure if that is the one to which you refer. It is certainly achingly beautiful nonetheless.