This might be difficult. I'll resist the temptation to say "EVERYTHING!" for some bands and just pick their awesomest songs.
Nevermore - Garden of Gray, Dreaming Neon Black, I, Voyager, Born
WoY - Will To Give, Allure, Dragged, Ghosts of Summers Past
Amon Amarth - Down the Slopes of Death, Masters of War, Seigreicher Marsch, Burning Creation
Moonspell - Wolfshade, Alma Mater, Full Moon Madness, Everything Invaded
Anathema - Fragile Dreams, Release
Arcturus - To Thou Who Dwellest In The Night, Wintry Grey, Ad Absurdum, Shipwrecked Frontier Pioneer
Megadeth - Loved To Deth, Rattlehead, Black Friday, Holy Wars, Elysian Fields
Overkill - Overkill, Blood Money, Elimination, Old School
Opeth - To Bid You Farewell, The Drapery Falls, April Ethereal
Drudkh - Wind of the Night Forests
Witchery - Unholy Wars, Plague Rider, Dead, Hot and Ready, Wicked
Evergrey - Solitude Within, She Speaks To The Dead, As I Lie Here Bleeding, The Essence of Conviction, In The Wake of the Weary
Keep of Kalessin - The Black Uncharted
Collide - Wings of Steel, Crushed, Violet's Dance
Genitorturers - Sin City
Loreena McKennitt - Mummer's Dance, Two Trees, Caravanserai
A Perfect Circle - The Hollow, 3 Libras, Blue, Gravity
Pearl Jam - Honestly....all of Ten
Ra - Only, Sky, Walking and Thinking
It's 3 in the morning and that's all I care to list for now....if I kept going I'd write a freakin' novel.