So longer than ten minutes and by someone more obscure than Chopin or Liszt.....

Have a look at:
Alkan - Sonata Quatre Ages, Symphony for Solo Piano, Concerto for Solo Piano
Busoni - Fantasia Contrapuntistica
Czerny - Sonatas (Czerny isn't obscure, but these are)
Agnew - Sonatas
Arensky - Pres Le Mer
Bortkiewicz - Ballade & Elegy
Bowen, Sonatas or Fantasia
Del Tredici - Mandango
Hinton - Variations & Fugue on a Theme by Grieg
Hough - Sonatas
Gould - Transcription of the Siegfried Idyll
Kodaly - Dances of Marosszek
Liebermann - Variations of a Theme by Schubert
Muczynski - Desperate Measures (Paganini Variations)
Poulenc - Suite or Suite Francaise
Reger - Variations and Fugue on a Theme by JS Bach
Roslavets - Sonatas
Rzewsky - The People United Will Never be Defeated
Sorabji - Lots of things
Stanchinsky - Sonatas
Szymanowsky - Sonatas
Tausig - Das Geisterschiff
That should get you started....