Beautiful Classical Smaller Pieces, duo,trio,etc

+1 Borodin Quartet #2
Schubert Quartet #14 D810 The Andante movement starts out as a death march and changes to different expressive moving moods throughout, the 2nd a lilting sweet violin expressing something lighter, and more hopeful maybe, I've always wondered. Usually a movement stays within a certain context or mood but this one does not, it is really brilliant, never heard anything quite like it as it is so completely unpredictable. Wonder what he was thinking when he wrote it? This piece had such a profound impact on me when I first heard it that doesn't diminish on subsequent listening.

Think about it Tubegroover, Schubert had written more now acknowledged masterworks by his death at 31 than Beethoven or almost any other composer had by that age.
No less a figure than Brahms, who may well have been the most learned of all composers, with the music of 400 years at his fingertips, said Schubert was the greatest composer who ever lived.

Well Schubert I'm not one for deciding good, better or best of anything, it's more a parlor game than anything BUT Schubert's string quartets are so very special as a genre of music by a single composer that, to me at least, as a body of work they have such a unique special character that can't be decribed or put into words, just an amazing accomplishment for a single human being. His deep sensitivity is keenly projected in his music. He isn't alone but he certainly is quite special in his own unique way. If Brahms say he isn, well I sure wouldn't argue with that!

The other make changes and develop themes.
Schubert comes at you from 20 directions at once and they are all related .

Many great suggestions. Glad to see mention of the Nielsen Quintet and of
Janacek, one of my favorite composers. Janacek's "Mladi"
(Youth) for wind sextet is a gem and highly recommended. Schubert's
"The Shepherd On The Rock" for soprano, clarinet and piano is
one of my favorite chamber works; as is his "Octet" for winds
and strings. Poulenc's "Sextet" for piano and winds is fantastic.
Prokofiev's "Sonata" for flute and piano. In a more modern
vein (beauty is in the eye/ear of the beholder):

Ligeti, "Ten Pieces" for wind quintet.
Elliot Carter, "Sonata" for flute, oboe, cello and harpsichord.
John Adams, "Road Movies" for violin and piano.