The Best Piano Works of the 20th Century

Speaking of Shostakovich, an addition to the many great nominations already made would have to be his “24 Preludes and Fugues”.  Inspired by a visit to J.S. Bach’s home this work is in the mold of Bach’s “The Well Tempered Clavier” in that it offers one prelude and fugue in each of the twelve major and minor keys.  Anyone new to this work should probably start with the recording by Tatyana Nikolayeva (Hyperion) who premiered the work.  

Two nominations for hidden gems would be another Bach inspired work, Ferrucio Busoni’s “Fantasia Contraputtista” and Leos Janacek’s “In The Mists”.  

Since Jazz has been mentioned, I would second the nominations of the Ravel piano works for, not only their greatness in their own right, but also their profound influence on improvising pianists, most notably Bill Evans.  

Hyperion released an extensive 'The Romantic Piano' series. Much of it is 20th Century. The Godowski 'The Complete Studies on Chopin's Etudes' 
is worth having. As far as the best, one can't ignore the Shostakovich  Piano Quintet.

Glen Gould playing "Goldberg Variations" by Bach.

@fixedincome---I too love the GV, but that is hardly a 20th Century piano work!