Scriabin wrote a romance for horn and piano which I think could be beautifully transcribed for trumpet. It is early Scriabin so it's lush and late romantic.
Might also take a look at some of the early Baroque and Renaissance works, some of which were for trumpet and harpsichord, or trumpet and organ (but with the organ part adaptable to piano). Folks such as Clarke or Purcell, etc. Maybe even some Haydn.
There's the Hindemith Sonata for Trumpet and Piano, it's early 20th but a real chamber work.