My today's favroites for that kind of mood:
- F. Chopin - "Nocturne in C-minor, "Nocturne op. Posth." and "Waltz No. 14 op. Posth.";
- J. S. Bach - "Piano Concerto no. 5 in a-Minor"
- L. van Beethoven "Moonlight Sonata";
- P. I. Tschaikovsky "Barcarole op. 37b";
- E. Grieg "Solveigs Song";
- L. Einaudi "Primavera";
- R. V. Williams - "Fantasia on Greensleeves";
- S. Rachmaninoff - "Piano Concerto no. 2, 1. movement"
- P. Broderick - "Diverge";
If I'm sad, I usually listen to sad music (I know that makes no sense) XD But yeah, I listen to Bach's Ciaconna from his Partita No. 2 in d-minor for unaccompanied violin. Or I listen to Walton's or Gubaidalina's Viola concerto (although that one's more creepy than sad).