Liszt B min. Sonata
Beethoven Op.111
Chopin Piano Concerto No.1
Chopin Grande Polonaise for Piano and Orchestra Op.22
Scriabin Etude Op.8, No.12 in D# minor
Scriabin Etude Op.42, No.5 in C# minor
Chopin Scherzo No.3 in C# minor
Chopin Ballade No.4 in F minor
Rachmaninoff Rhapsody on a theme of Paganini
Rachmaninoff Piano Concerto No.3
Rachmaninoff Sonata No.2
Beethoven Op.106 'Hammerklavier' Sonata
Brahms Symphony No.4
Mahler Symphonies (all 9 of them)
Liszt Mazeppa
Liszt Mephisto Waltz No.1
Balakirev Islamey
Ravel Gaspard de la nuit
Liszt Spanish Rhapsody
Liszt Hungarian Rhapsodies Nos. 2, 6, 11, 15, 19
Mendelssohn Songs Without Words
Beethoven 'Moonlight' Sonata
Liszt Feux Follets
Liszt La Campanella
Schumann Carnaval
Grieg Concerto in A minor
Grieg Ballade Op.24 in G minor
Sorabji le jardin parfume
Chopin Sonata No.3 in B minor
Chopin Sonata No.2 in Bb minor
Grieg Peer Gynt Suite
Bach Goldberg Variations
Bach Keyboard Concerto in D minor
Scriabin Sonata No.10
Scriabin Vers la Flamme
and...
Sorabji Opus Clavicembalisticum, I'd assume.
There are MANY more, these are just the ones I remember offhand.
This is just as hard to answer as all the other threads of the 'What is the most ...?' variety. I give you credit for at least not starting a 'What's hardest?' thread.
Phil