Quite an admirable list!

Bela Bartok - His six string quartets are pure indulgence, very dynamic and visceral, sometimes bordering on violent
Claude Debussey - I'm not terribly much for his symphonic work, but I haven't heard a piano piece by him that I didn't love
Dimitri Shostakovich - His symphonies are dark and brooding, just the way I like them, especially his 8th symphony. One of the best and most prolific String quartet composers of the modern era.
Ludwig Van Beethoven - Mainly for his Piano sonatas, Moonlight, Pathetique, and Apassionata are without a doubt my favorite pieces of music, full stop.
Frederich Chopin - In my opinion, next to Beethoven, the greatest piano composer ever. His Nocturnes are beyond my description.

Superb list! Although I prefer Liszt to Chopin.

definitely need to check out some Shoskatovich

any recs?

Schoenberg (early rather than later)
Stravinsky (later rather than early)
Mahler
Delius - for his control of melody alone he had to make the list.
Prokofiev

Vivaldi
Bach
Mozart
Brahms
Beethoven

Excellent stuff, I love everything there! I'm going to add Fiocco into the mix, because he composed some very original and highly complex harpsichord pieces which to this day I've heard none more innovative.

Definitely check out his Symphony No. 8 in C Minor. It's one of my favorite symphonic pieces ever:

The Jazz Suites. And Tahiti Trot!

In no particular order

Tchaikovsky
Vivaldi
Satie
Mozart
Howard Shore (a modern film composer)

Chopin
Tchaikovsky
Mozart
Beethoven
Debussy