When I’ve remembered to do it, I’ve tagged some instrumental tracks on Last.fm. Some are straight-up instrumental metal songs; some are intros, outros, acoustic pieces, oddities, etc. Maybe you’ll find something worthy:
Agalloch - A Celebration for the Death of Man...
Agalloch - Odal
Agalloch - Our Fortress Is Burning... I
Agalloch - Our Fortress Is Burning... III: The Grain
Agalloch - The Hawthorne Passage
Agalloch - The Lodge
Agalloch - This White Mountain on Which You Will Die
Animals as Leaders - CAFO
Arch Enemy - Demoniality
Arch Enemy - Snowbound
Arch Enemy - Stigmata
Arch Enemy - The Ides of March
Arch Enemy - Vox Stellarum
At the Gates - Into the Dead Sky
At the Gates - The Flames of the End
Be'lakor - Husks
Before the Dawn - Deliverance
Cannibal Corpse - From Skin to Liquid
Cannibal Corpse - Relentless Beating
A Canorous Quintet - The Last Journey
Corrosion of Conformity - Bottom Feeder (El Que Come Abajo)
Craft - 616
The Crown - Dream Bloody Hell
The Crown - In Memoriam
Dark Tranquillity - Ex Nihilo
Darkane - Maelstrom Crisis
Daylight Dies - Dismantling Devotion
Death - Voice of the Soul
Decrepit Birth - Darkness Embrace
Decrepit Birth - Sea Of Memories
Dissection - Crimson Towers
Dissection - Feathers Fell
Dissection - Into Infinite Obscurity
Dissection - No Dreams Breed In Breathless Sleep
Enforcer - Crystal Suite
Gorgoroth - Domine in virtute tua laetabitur rex
The Haunted - Dark Intentions
The Haunted - Demon Eyes
The Haunted - Privation of Faith Inc.
Helrunar - Hornung
Helrunar - Winter
In Flames - Acoustic Medley
In Flames - Dialogue With The Stars
In Flames - Timeless
In Flames - Wayfaerer
Insomnium - Resonance
Loits - Sinimäed 1944
Metallica - Orion
Metallica - The Call of Ktulu
Metallica - To Live is to Die
Mistur - Mistur
Mors Principium Est - Lost beyond retrieval
Mors Principium Est - The Glass Womb
Nader Sadek - Nigredo in Necromance
Naglfar - The Infernal Ceremony
Nile - Dusk Falls Upon the Temple of the Serpent on the Mount of Sunrise
Nile - Spawn of Uamenti
Nile - The Infinity of Stone
Nine Inch Nails - A Warm Place
October Falls - Viima
October Tide - A Nighttime Project
October Tide - Dear Sun
Old Man's Child - In Quest Of Enigmatic Dreams
Old Man's Child - Wounds From The Night Of Magic
Opeth - Ending Credits
Opeth - Epilogue
Opeth - For Absent Friends
Opeth - Patterns in the Ivy
Rapture - Completion
Rapture - For the Ghosts of Our Time
Rapture - Intro
Rotting Christ - Fethroesforia (Instrumental)
Rotting Christ - Sanctimonius
Satan's Wrath - Galloping Blasphemy
Satyricon - Transcendental Requiem of Slaves
Soilwork - Centro De Predominio
Soilwork - Entering The Angel Diabolique
Unreal Overflows - Under the Quiet Silence
Unreal Overflows - Unexpected Dimensions
Watain - Dead but Dreaming
Watain - Lawless Darkness
Watain - Withershins
Witchery - Disturbing The Beast
Witchery - The Wait Of The Pyramids
Witchery - War Piece