Well, Robert, here's my must have list. I have intentionally left out my
suggestions for performances as this gets so subjective.

1. A set of the Beethoven symphonies.
2. Britten: War Requiem
3. Faure: Requiem
4. Bach: Goldberg Variations
5. Bach: Brandenburg Concerti
6. Barber: Violin Concerto
7. Brahms: Four symphonies
8. Debussy and Ravel: String Quartets
9. Ockeghem: Missa pro defunctis
10. Lassus: Prophetiae Sibyllarum
11. A good collection of English Madrigals
12. Rismky-Korsakov: Scheherezade
13. Bruckner: Symphony 7
14. Dvorak: Symphony 9
15: Schumann: Piano concerto
16. Mendelssohn: Midsummer Night's Dream
17. Shostakovich: Symphony 5
18. Brahms: Ein Deutsches Requiem
19. Bach: Mass in b minor
20. Tchaikovski: Swan Lake
21. Stravinsky: The Rite of Spring
22. Wagner: A good overture/prelude collection
23: Chopin: Nocturnes
24. Verdi: La Traviata
25. Puccini: La Boheme

These are but a random sampling of thousands of wonderful works that you
will hopefully encounter.  I am sure that you will delve deeper and I know
that you will get a wide and diverse set of lists from this crowd.  Happy
exploration!

Kevin Sutton