I like Adagio for strings too. I would also add to the list Vivaldi's Concerto for Two Violins in A Minor.Samuel Barber's Adagio for Strings is my favorite, I love the harmony and the overwhelming climax that it builds up to. If I want to quiet my mind and become grounded, I just play this song on repeat.
Thanks for answering Mathwonk!you implicitly asked 2 questions:
1) what is your favorite classical piece (of muisic)
2) what is your favorite classical music to listen to while doing math.
I like bach's cellos suites to listen to alone, but i find western classical music distracting while thinking about math [mozart demands ones attention], so i prefer indian classical music for doing math, such as ali akbar khan: pre dawn to sunrise ragas, or anything by bismillah khan. i also have some very ethereal flute tapes made by friends of mine.
It's one of my favourites too; Again, I've played it with orchestra in rehearsal and performed the first movement in a concert of single concerto movements, back in 2002.The Grieg Concerto for Piano and Orchestra in a, Op. 16 is currently my favorite piece of music, but it changes, naturally, over the years.
Above is the first part of the wonderful performance (and recording) by Krystian Zimerman. Obviously, if you follow the logical "recommendations" on youtube, you'll be able to navigate to the 2nd part of the first movement, then the 2nd and 3rd movements of the piece.