I am a huge fan of Dmitri Shostakovich. He was a Russian composer who lived in the 20 century, for those who haven't heard of him.

I have never heard music as expressive as his. His life was fairly horrible, mainly at the hands of the Soviet government, and his music is an audible expression of highly distilled hatred and misery. His complexity rivals Mozart, and his expressiveness rivals Schubert and Brahms. Give him a listen if you haven't already, his fourth or sixth symphony is a good starting place.