There's always Sorabji, about whom opinions vary widely but whose music I've enjoyed in limited hearings.
Strongly agreed on Hindemith.
Nancarrow's Three Canons for Ursula (for regular piano) is interesting.
Rodion Shchedrin is an excellent pianist as well as composer; he wrote a Polyphonic Notebook and a set of 24 Preludes and Fugues. I like his music but some dislike his politics (rather cozy with the Kremlin in the USSR era).
In the composer/pianist category, is Busoni's Fantasia contrappuntistica too old to count? Busoni's music definitely deserves attention.
Funny thing about the Shostakovich P&F: I enjoy them, but in the old days when I used to read rec.music.classical.recordings, a number of the Usenet savants regarded them as practically pianistic doggerel. But I suspect many of said savants also waxed enthusiastic about Joyce Hatto's pianism (I'd given up Usenet by the time that hoax was exposed).