There are not enough Russians in this thread!
My first recommendation goes to Taneyev's Piano Quartet in E major Op. 20, his Piano Trio in D major Op. 22, and his Piano Quintet in G minor Op. 30. These are substantial works of great depth and structure. (Taneyev premiered Tchaikovsky's first piano concerto and completed his 2nd and 3rd concertos, and the major Russian chamber music competition is named for him, so he was well recognized in his own country, even if we've forgotten him now.)
Borodin's Piano Quintet is a fully engaging and enjoyable work. The Marco Polo CD that presents it with other Borodin chamber music is excellent!
I must mention cello sonatas, which are among my favorite chamber form. The two cello sonatas of Myaskovsky are very good indeed - beautifully melodic, melancholy, rhapsodic. One or more of them is often paired with his exquisite cello concerto or with Rachmaninoff's beautiful cello sonata.
Finally, my non-Russian choices. There are several CDs that couple the chamber music of Respighi with that of his teacher, Martucci -- piano quintets, cello sonatas, violin sonatas, etc. When I first heard these, I was surprised and delighted at just how good they are.