Sonata: maybe Beethoven's op 90, or op. 10, or Mozart's op. 330
Etude: some of the easiest chopin etudes
Prelude/Fugue: WTC II 14, WTC I 20
And, from another style, I would try Castilla or Sevilla from Albeniz's Suite española, or Liszt's Valse Oubliee 1, or a Chopin's difficult nocturne. And you can also try some Mendelssohn's Songs without words.