There's an Italian music critic who compiled a list of the GREATEST works of the mid-late 20th century, and it's quite a broad palatte, taking in classical, jazz and rock. Here's his list of the Top 20, in case anyone's interested:
Most significant works of music 1950-1990 1. Shostakovic: Symphony No 15 (1971) [classical]
2. Karlheinz Stockhausen: Gesang der Junglinge (1956) [classical]
3. John Coltrane: A Love Supreme (1964) [jazz]
4. Captain Beefheart: Trout Mask Replica (1969) [rock]
5. Boulez: Repons (1980) [classical]
6. Carter: Symphony of Three Orchestras (1977) [classical]
7. Ligeti: Double concerto (1972) [classical]
8. Lutoslawski: Sinfonia 3 (1983) [classical]
9. Charles Mingus: The Black Saint And The Sinner Lady (1963) [jazz]
10. Part: Tabula rasa (1977) [classical]
11. Penderecki: Hiroshima Threnody (1960) [classical]
12. Velvet Underground & Nico (1967) [rock]
13. Gerhard: Concerto for Orchestra (1965) [classical]
14. Balakauskas: Ostrobothnian Symphony (19xx) [classical]
15. Terry Riley: Rainbow in Curved Air (1968) [electronica]
16. Jon Hassell: Dream Theory In Malaya (1981) [electronica]
17. Meredith Monk: Dolmen Music (1981) [classical]
18. John Fahey: Fare Forward Voyagers (1971) [folk]
19. Albert Ayler: Witches and Devils (1964) [jazz]
20. Sun Ra: Atlantis (1967) [jazz]