If you want to begin with readily approachable 20th Century music featuring
the piano, I would suggest:

Prokofief, Piano Concertos #1 and #3
Bartok, Piano Concerto #3
Ravel, Concerto for the Left Hand and Concerto in G
Poulenc, Piano Concerto, Concerto for Two Pianos, Aubade
Britten, Piano Concerto
Shostakovich, Piano Concertos #1 and #2
Menotti, Piano Concerto

Jim Tobin