Béla Bartók (1881-1945) essentially influcenced the evolution of modern classic in the beginning of the past century. He succeded in merging impressions from his homeland (hungary and from the balkans) with intonations of the radical modern age (Strawinsky and Schönberg).
You can get a survey of his musical/artistic works in the 153 pieces (sorted by difficulty from easiest to hardest) for piano - the so called "Mikrokosmos"