So far a lot of recommendations for the Bartok-Shostakovich sets.  No
objections, but if nobody's mentioned these, I'd like to add the following
to the 20th-century string quartets thread:

Ravel's - probably my all-time favorite quartet
Bloch's - tremendous, epic works
Martinu's - my ideal of quartet writing
Hindemith 3rd - with a great, quirky slow movement
Simpson's - pieces with an incredible symphony-scaled reach
Schoenberg 2nd - beautiful and poetic, mostly pure 19th-century tonal
Piston's - bright and clean
Foss 1st - a highpoint of neoclassicism
Thompson 1st - lovely, folk-based melodies
Vaughan Williams - not great quartets, but a charming first and a brooding
second
Holmboe - see Piston
Rosner - "big-shoulder" quartets
Vainberg - in a class with Shostakovich and in a similar idiom
Bacewicz - wonderful; strongly influenced by Bartok
Nielsen - refreshing, convivial
Ginastera - there are three.  I've heard one and two - Bartok does the
samba.

Steve Schwartz