Like any list or ranking, there will always be a subjective element involved. However, after consulting numerous lists of this type, looking at the literature, and using my personal expertise (Music History and Literature degree after all), a fairly decent list can be arrived at.
Full Disclosure: Since the defense of the Judeo-Christian and classical (Greco-Roman) heritage is the primary purpose of this site, it will be abundantly clear to the discerning reader that the western music that reflects this will take priority, and the departure from this heritage that started in the 19th century and later requires more “stinginess” if you will.
Essential Works for Western Music Literacy (recommended recordings will be added as time permits).
Bach, Johann Sebastian (1685-1750)
Brandenburg Concertos 1-6
Orchestral Suites (Overtures) 1-4
Mass in Bminor
St. Matthew Passion
Organ Works, especially the Toccata and Fugue in Dminor, Chorale Preludes, and the Passacaglia and Fugue in Cminor
The Well-Tempered Clavier
Beethoven, Ludwig van (1770-1827)
Symphonies 1-9. Good sets can also be found here, here, here, and here.
Piano Concerti 1-5.Two other good sets can be found here and here.
Piano Sonatas. There are 32, so there are some discs which have only the most famous which are readily available.
Brahms, Johannes (1833-1897)
Piano Concertos 1-2
A German Requiem
Solo Piano Music (especially Variations on a Theme of Handel, Op.79 Rhapsodies)
Handel, George Frederic (1685-1759)
Messiah. Recordings here and here are also quite good in lieu of the Pinnock.
Israel in Egypt
Royal Fireworks Music
Julius Caesar (Gulio Cesare)
Haydn, Franz Joseph (1732-1809)
Symphonies (Over 100 of them, but especially the 12 London Symphonies, 6 Paris Symphonies, and the “Farewell”
String Quartets, especially Op.71, 74, 76, and 77
Magnus Liber (Sacred Organum)
Sacred Music (Motets, Masses, etc…)
Mozart, Wolfgang Amadeus (1756-1791)
Piano Concerti, especially 10, 19–27
Symphonies, in particular 25, 29, 35-41
The Marriage of Figaro
Eine Kleine Nachtmusik (Serenade no.13)
Horn Concertos 1-4
Ockeghem, Johannes (C1420-1497)
Sacred Music (organum)
Scarlatti, Domenico (1685-1757)
Sonatas for Keyboard