oooh, a classical thread!
JS Bach is an old favorite.
My first non-baroque favorite was Bartok's Concerto for Orchestra. That was followed a couple of years later by The Rite of Spring - that one I had to get to know for an assignment and it too days of playing it on repeat to get my thick skull to recognize it as music. 
Recently into Faure's piano quartets. Actually, chamber and concertos are relatively new for me, as I used prefer (by far) straight orchestral..... Rachmaninov's piano concerto no 2 is breathtaking and hoping to listen to more quartets and quintets soon.
Also been checking out Kathryn Stott's recordings lately, which got me listening to Howell's Three Dances for violin and orch, as well as Koechlin's Les Heures Persannes.
And not long ago, I started working through a big box set of the Kronos Quartet, and from there I'm still listening to Arvo Part's Missa Syllabica, Osvaldo Golijov's Dreams and Prayers of Isaac the Blind, and Terry Riley's Cadenza on the Night Plain. They are good for shoo-ing away people who might otherwise want to stick around and have a conversation. :rollhappy:
