Mozart's Requiem Mass, so well-known to all, remains one of the most powerful and sublime among those ever composed (Fauré's a close second). Most apt music on this Hallow's Eve. My recommendation: as dusk descends and the wind rises and all becomes cold without, light the tealight in your jack-o-lantern, start a crackling hearthfire, and play the work at full volume while meditating on your mortality between sips of hot mulled wine.