The European 20th Century Masters

Shostakovich (1908-1975) was an extremely influential composer in music history of this time. He had a close connection to the Stalin regime, meaning that all music had to be "accessible to the workers", so therefore much of his music and melodies are very simple. He spent his life suffering because he felt his compositional integrity had suffered. He wrote many pieces for the piano including 2 piano sonatas, 24 preludes Op. 34, and 24 preludes and fugues Op. 84 (the most famous being the prelude and fugue in d minor). There are very contrupuntal pieces that mimicked the works of Bach.
Alberto Ginastera (1916-1983) also added his flavor to compositions of the 20th century primarily through his first piano sonata which best portrays his style. He also composed a suite of criollas dances, a set of Argentina dances, 12 American preludes as well as some other compositions.
Stockhausen (1928-present) was a piano student of Messian and a very structured worker in his composing. Everyday he would work from 10:30-1:30pm, then 3:00pm-7:00pm, then 10:00pm-12:00am. He was a problem solver and a thinker. He ventured into the area of electronic music and composed very heavy serial music. He had his own notational system and had an "aleatoric" style (latin being the world for chance).
Messian (1908-1992) was a very profound and unique composer. He literally saw colors as effects of different sounds and combinations of sounds. He wrote a great deal for the piano, perhaps the most famous works being his 20 Vingt Regards sur L'Efant Jesus. He invented his own musical language that was heavily influenced by Debussy (the sounds and sonorities) and Stravinsky (freedom of meter). Messian also used additive rhythm where he would bring the fibonacci sequence, or prime numbers, into the amount of note values for give passages of music. In 1942 he published his own book on his musical style stating that harmony was color, and not directional.