Blegging time: Classical music requests

Time to pick the brain of classical music lovers: my listening habits for years have trended to operatic and symphonic music, almost exclusively. I listen to almost no chamber music, and I’m looking to change this. So I’m looking for recommendations: what’s some awfully good chamber music?

Don’t bother recommending the Mozart or Beethoven string quartets — I know about those, even if I don’t own them yet. And I’m talking pure chamber music here, not concertos. Thanks!