It depends really on what kind of piano music you like. If you want something that is really lyrical and sets your heart on edge, go for the poetic mastery of Chopin. He was torn away from Poland during the war, and much of his music focuses on his love and grief for his homeland and it can be totally heartbreaking.

If you're looking for the dazzling and virtuosic, I'd recommend Rachmaninov certainly, but do have a look at Lizst. Lizst was a phenomonal pianist himself, and wrote music that often only he could play. His version of the prelude from Tristan und Isolde by Wagner is breathtaking.

Some people underestimate the pianistic writing of Beethoven and Mozart, and they're certainly worth a look - particularly early Beethoven or late Mozart, which were written at around the same time.

Personally though, nothing will ever beat the French masters for me. Listen to some of Debussy's famous piano works for their dreamy, otherworldly qualities. Also, Maurice Ravel was an absolute god at writing for the piano and has written some of the most beautiful piano pieces.

Aside from the classical, listening to some of the early ragtime or jazz pianists is always an education. Go searching for Joplin or Jelly Roll Morton.

Hope I was of some help.