The Best Piano Works of the 20th Century

Gershwin's "Rhapsody in Blue", a uniquely American piece always has to be included in 20th century piano music. I agree with all of gregm's choices less  the Massiaen piece but will sure check it out! The impressionistic work Clair de lune by Debussy  would be on my list as well, less clear is when it was penned.

Bdp24 if you enjoy the solo piano version of "Pictures", I highly recommendd the Evgeny Kissen recording on RCA.