Beautiful Classical Smaller Pieces, duo,trio,etc

Neo classical quartets:
Kronos
Balanescu;

Tango: Quintet Buenos Aries

The Julian (Bream) and John (Williams) guitar duo albums are great (Assad Bros. duo also excellent).
Violin/Piano: I like the Prokofiev Sonata #2 (originally flute) and the Saint-Saens Sonata #1.
String Quartets: Debussy or Ravel (Guarneri has a fairly recent high-quality LP of the Ravel w/two movements per side).
String Quintet: Schubert Quintet in C--give me heaven before I die

Excellent chamber music performances in superb sound - some specific recommendations among many more:

Yarlung 95990-787V - Petteri Iivonen, violin, and Kevin Fitz-Gerald, piano: Music of Ysaye, Debussy, Bach and Lefkowitz - Available from: http://www.yarlungrecords.com/180.html#

Yarlung 09261-819V - Ciaramella: Dances On Movable Ground - Renaissance & Baroque dance tunes - Available from: http://www.yarlungrecords.com/180.html#

Philips 835393/4 AY - Schubert Piano Trios, Beaux Arts Trio

Philips 4769648 - Rossini Sonate a Quattro: Nos. 1-6, Accardo, S.Gazeau, A.Meunier, F.Petracchi

Hyperion A66171/A66172/A66173 - The Chamber Music of Malcolm Arnold, Volumes 1, 2 and 3 - Nash Ensemble
.

Quatuor pour la fin du temps ("Quartet for the end of time"), violin, cello, clarinet, piano
(1940–41) Olivier Messiaen

As Tostadosunidos said above, the John Williams, Julian Bream double album is great and one of my favorites in my entire collection. Beautiful guitar work by two masters of the instrument. Its a live recording on RCA and it puts you right in the recording venue. As your system improves, so does this wondrous recording. Here's what you'd be looking for:

http://www.ebay.com/itm/Julian-Bream-John-Williams-Live-DOUBLE-LP-1979-EX-/111690932246?pt=LH_DefaultDomain_3&hash=item1a014c6016

Happy listening ...