Among Naxos American classics, I recommend Charles Tomlinson Griffes'
remarkable piano sonata.

Also I much enjoyed a recent release of string quartets by Gloria Coates -
unique stuff, needs some listening- what doesn't? It is almost all based
on glissandos.  I would like to hear her symphonies as well.  Years ago
I heard on fm, her "music for open strings" and never forgot it.

T0 the lists submitted thus far (including Steve Schwartz' extensive one)
I would add

   Roger Sessions - (Third Symphony for example)
   Ingram Marshall

Bernard Chasan