Dvoraks American and New World are both GREAT classics and close to my own heart being respectively the first unabridged string quartet and symphony I ever had the pleasure of performing: they are the reason I have such a love for classical
music! You haven't LIVED until you've played the New World with a 100 piece symphony. . .
That said, I love Shostakovitch. His 5th symphony and 8th string quartet are among my favorites.
Barbers Adagio for strings is a beautiful, timeless piece.
I really enjoy performing works by Sibelius, Tchaikovsky, Beethoven (again, you haven't lived. . .oh man. . .)
My favorite solo/concerto pieces to listen to and perform are some of the Vivaldi violin concertos, the Brahms Sonatas (viola), Bach Cello suites (on the viola), J.C. Bach c-minor for viola. . .I could go on.
Oh and Mendelssohn. And Rachmaninoff. . .