If I had to pick a single song, it would be Iron Maiden’s Dance of Death.
My full playlist looks something like this:
Iron Maiden: Seventh Son of a Seventh Son (full album), Paschendale, Dance of Death, the Mercenary, the Trooper, the Pilgrim, and These Colours Don't Run, and the Longest Day
Metallica: All Nightmare Long, Enter Sandman, Disposable Heroes, Battery, the Unforgiven Trilogy, Am I Evil? and Wherever I may roam.
Tristrania: Beyond the Veil, Widows Weeds, World of Glass (all full albums)
Nightwish: Nemo, Amaranth, Master Passion Greed, and Seven Days to the Wolves
Epica: Unleashed, Storm the Sorrow, Karma+Monopoly on Truth, the Divine Conspiracy, Design your own Universe, and Avalanche.
Evanescence: Haunted, Tourniquet, Whisper, and Sweet Sacrifice (because after all, “we’re all a little insane”, especially after the eighth ilvl 63 weapon you identify with base damage <400)
Occasionally I throw in something like Iron Man or Bark at the Moon, for a little comic relief since I can’t take Ozzy seriously.