Short list of the most beautiful music ever written.
In Chronological Order of Composition:

Gregorio Allegri				Miserere Mea			
Thomas Tallis					Spem in Alium
Johan Sebastian Bach				Orchestral Suite #3, 2nd mvmt "Air"
Johan Sebastian Bach				Partita for Solo Violin #2, 5th mvmt "Chaccone"
Franz Josef Haydn				String Quartet #62, 2nd mvmt "Poco adagio - Cantabile"
Ludwig van Beethoven				String Quartet #13, 5th mvmt "Adagio molto espressivo" - Cavatina
Gustov Mahler					Symphony #5, 4th mvmt "Adagietto"
Claude Debussey					Clair de Lune
Jean Sibelius					Andante Festivo
Jules Massenet					Thais - Meditation
Gabriel Faure					Lux Aeterna - Requem
Edward Elgar					Cello Concerto - 1st mvmt
Edward Elgar					Enigma Variations - Variation #9 "Nimrod"
Samuel Barber					Adagio for Strings
Arvo Pärt					Spiegel im Spiegel
Morten Lauridsen				Les Chansons des Roses - Song #5 "Dirait on"
Karl Jenkins					The Armed Man (A Mass for Peace) - 12th mvmt "Benedictus"