Alexander Tcherepnin
Nikolay Roslavets
Nikolai Myaskovsky (particularly sonatas #2 and #3)
Myaskovsky is a special case because his music is well-known in Russia, albeit the later symphonic music that is more accessible. His early sonatas should be performed more often. Like Tcherepnin, Myaskovsky suffers from Murray McLachlan syndrome (which is when great pieces are available on CD only from that mediocre pianist, or can be found without him only on obscure live discs or on historical LPs).
Contrary to what some have said, Tcherepnin IS vastly underrated. The online reviews I've read have been condescending and dismissive. For instance, his masterpiece of a symphony, #3, is routinely dismissed as a "weak attempt to imitate Chinese culture". I've read three reviews of the symphony, and each of them uses the work's pentatonic flavor to discredit it, as if it's a crime to not be Chinese and to not make a carbon-copy of Chinese classical music. It's a matter of fact, to me, that the Tcherepnin 3rd symphony is one of the greatest symphonies ever written.
The Tcherepnin 5th concerto is superb, and I'm going to order the #2/#4 disc soon.