Most achingly-beautiful music

Another addition to the list, Dvorak's "Mesicku na nebi hlubokem" (O Moon High Up in the Deep Sky), from Act 1 of Rusalka. I'd heard this before from time to time but didn't know who wrote it until I heard it played at Dvorak's home in the Czech Republic. Bought the disc on the spot. Simply beautiful.

I have to concur with those who submitted Barber's Adagio for Strings. It sort of troubles me that this music was introduced to many people in popular culture in the sad, sad settings used in the movies The Elephant Man and Platoon. I grew up listening to Barber's Adagio in Germany in the '60's because my mother liked it. I never thought of the Adagio as sad as such. In fact, later on in life when I rediscovered it and before those movies used it, I thought of it as quite sensual. Apparently, I am not alone because a former principle dancer from the Royal Danish Ballet, Fleming Halby, choreographed a somewhat erotic pas de deux to the Adagio.
Let me also submit Camille Saint Saens' C Minor (Organ) Symphony.
Also, the andante asai movement (2nd) to Ravel's piano concerto in G-as someone else already mentioned in this thread.
Pulenc, Concerto for Organ, Strings, and Timpani
Bach, B Minor Mass
Bartok, Concerto for Strings, Percussion, and Celeste
Brahms, Double Concerto for Violin and Cello
Mozart, Requiem
Brahms, Violin concerto
Schubert, 9th Symphony (The Great)

Pilgrim's Chorus from Wagner's Tannhauser

Dwpc...and what do you think of the Tannhäuser overture?
One of the most sensual-erotic music that has ever been written, I think.

Detlof...not too detract from the overture; the Pilgrim's Chorus is more concentrated. IMO, the two "allelulea"'s and pulsating strings at the close of the chorus, though brief, are about as good as musical moments get.