I'm not all that familiar with the work of the Guarneri Quartet. I heard them only once, in the early 1980s, and all I remember is they sounded annoyed and out of sorts. On record, I have their Beethoven cycle, which is well-played and very middle-of-the-road, not quite the thing for someone who likes extreme Beethoven.
However, they've been a fixture on the scene for decades and are now in their last season of performances, having announced their retirement at the end of 2009. Sony has made a number of albums that appeared only on LP available digitally, meaning these are recordings that were long, long out of print. They're being distributed by Sony as downloads (available at iTunes and Amazon, for example) and at ArkivMusic as CDs. You can find these albums on a special page at Arkiv. The sets include works by Bartok, Brahms, Mozart, Mendelssohn, and others; very tasty repertory. In addition, the Guarneri is releasing a new recording, called The Hungarian Album, which features works of Dohnanyi and Kodaly. That is also delicious.
My only question: are they recording the big Octet William Bolcom wrote for them and the Johannes Quartet?? That would be a fitting capstone to a long career.
[Corrections posted Monday, Feb. 9]