Well, I'm willing to wager your ears are even bigger than mine, so I'll throw in a few things that aren't necessarily my cup of tea, but you might find interesting.

Shostakovich: Complete String Quartets - Emerson String Quartet

Starts out as tonal as Shostakovich ever gets (with Number 1), and end up going to some pretty crazy and dark places. Nothing like Stalinist Russia to bring out the sarcasm in someone.

No. 8 is the most Famous - here's the second movement.

Honorable mention goes to Sonata for Contrabass Solo by Mieczyslaw Weinberg, Op. 108 . A student and colleague of Shostakovich. I'm playing this piece for my master's recital, and there's a great recording on Spotify by Joel Quarrington (also probably available on itunes).

Charles Ives - Piano Sonata no.2 "Concord, Mass. 1840-60"

I have no idea why I like Ives' music. It is WAY out of my wheelhouse in a lot of respects. However, his chamber music is amazing, and the Concord Sonata is no exception.

Honorable mention goes to His Violin Sonatas, which Hilary Hahn recorded a while back. Fantastic recording, available on itunes etc.

Gyorgi Ligeti - Artikulation

One of many electronic pieces by this composer. Tried to find an album, but this stuff in't often sold in stores:

Honorable mention:

Schoenberg: Five Pieces for Orchestra - London Symphony Orchestra with Fred Sherry

Most of the music you're listening to on this list probably wouldn't have been made until much later if not for this guy. He solidified Serial atonal music from a theoretical standpoint, and was one of the first people to use it as a technique to write music.

Honorable mention: Webern - Six orchestral pieces

Student of Schoenberg, well respected in his own right. His opera, Wozzek, is probably one of the most commonly performed modern operas.

Pierre Boulez: Le Marteau Sans Maître

I hate this man. He is, however, well known for his advancement of multiple serialism, in which not just he notes, but rhythms, dynamics, etc. are all set up in serial patterns, derivatives of which are used to compose.

Honorable Mention:

Stravinsky: Rite of Spring (with the ballet if you can for the first listen)

I'm gonna be straight with you, while i love this piece, I legit can't listen to it after dark - it scares the shit out of me. This ballet's production (which is using the original choreography, i think)... doesn't help me with that.

Karlheinz Stockhausen: Elektronische Musik 1952-1960

My friend, you are going to dig the shit out of this.

Honorable mention:

Well, hopefully that will give you some stuff you like, and some composers to look more into.