Tristan und Isolde (AMEN ALBERICH!) - Wagner
(especially Isolde's Transfiguration, or Liebestod).
The Planets: Venus - Holst
Parts of Beethoven's 9th Symphony
The last scene of Die Walkure (The Valkyries) from The Ring Cycle - Wagner
Piano Concert No. 2, Opus 102, 2nd movement - Shostakovich
Adagio for Strings - Barber
also rescored for voices and called "Agnus Dei"
Moonlight Sonata, 1st movement - Beethoven
Appassionata Sonata, 2nd movement - Beethoven
Symphony No. 6, Mvmt II and V - Beethoven
Te Deum - Arvo Part (in fact, all of his music is fairly sombre)
Miserere - Part
Litany - Part
Spiegl im Spiegl - Part
Magnificat - Part
Parts of Requiem, Gloria, and Magnificat - John Rutter
Miserere - Allegri
In Ecclessi - Gabrieli
Cloudburst - Eric Whitacre
Little Tree - Eric Whitacre
Any music from the choirs of Cambridge University
Bits of La Traviata (depressing opera, pretty though) - Verdi
Rhapsody on a Theme of Paganini - Rachmaninov
Claire de lune - Debussy
Fantasie Impromptu (and any of his nocturnes as well) - Chopin
Clarinet Concerto in A: Adagio - Mozart
Piano Concerto No. 23, 2nd movement - Mozart
Try looking on www.classiccat.net
-Other composers: Palestrina, Gorecki, Taverner, John Corigliano, Joe Giorgiono
This kind of music exists in a lot of middle movements from symphonies and concertos. You just have to know where to look.
Happy listening!