Well, I don't listen to that much of the darker stuff, so let's see what I can scrounge up.  Because I listen to a lot of music from video games, I'm just gonna put the game name rather than the composer.

Suffer - Devil May Cry 3
Devil's Never Cry - Devil May Cry 3
Cursed Prison - Castlevania: Symphony of the Night
Clockwork - Castlevania series
Candlelight Fantasia - Symphony X
My Immortal- Gregorian
Liberi Fatali - Final Fantasy VII
Kiss Eternal - Lords of Acid
Down With the Sickeness- Disturbed
Bring Me to Life - Evanescence

There are a few others like Meaning of Life also by Disturbed, but that's the best list of 10 I can come up with.  Trying to keep a little diversity in there.

[RavenFreefall]

Mine Would Have to be....

Her Portrait In Black - Atreyu
Savior - Skillet
Hero - Skillet
Her Voice Resides - Bullet For My Valentine
Waking The Demon - Bullet For My Valentine
Pray For Plagues - Bring Me The Horizon
Amy Lee And Seether - Broken
Army Of Me - Chimaira
How Can I Live - Ill Nino
Have You Ever Felt - Ill Nino

1  -  Opeth - The Moor
2  -  Ne Obliviscaris - Forget Not
3  -  Bach - "Little" Fugue in G Minor
4  -  Nevermore - Who Decides
5  -  Opeth - To Rid The Disease
6  -  Nick Cave - The Mercy Seat
7  -  Strapping Young Lad - Velvet Kevorkian/All Hail The New Flesh
8  -  Devin Townsend Project - Coast
9  -  Porcupine Tree - Aesthetize
10-  Mastodon - The Last Baron

They're just my top 10 favourite songs/pieces right now, but they all seem pretty dark if that was what you meant by "monstrously". Colonial Boy, Triumph and Bad Devil, all by Devin Townsend, Life On Mars by David Bowie, Pour Another Icepick by The Mars Volta and a great big list of 100 other songs almost made it on there.

[Andrea Warfare]

Not only are these Monstrous songs they're also some of my favorite and I'd highly recommend them to you

1.Immortal Korruptor-Gwar

2.Return of the Fly-Misfits

3.Lycanthropy-G.B.H

4.The Horror of Party Beach-Sloppy Seconds

5.the Massacre-TheExploited

6.Rampton Song-Disorder

7.Bodies-Sex Pistols

8.There'll be no Tomorrow-Special Duties

9.No Escape-the Restarts

10.Led to the Slaughter-Varukers

[DARKNESS AWAKENED]

here is a few good ones some found by accident some are just bad ass songs
moonspell- wolfshade(awerewolf masquerade)
children of bodom- lil bloodred riding hood
killswitch engage- dayllight dies
lordi-would you love a monsterman
ozzy-waiting for darkness
diecast-medieval
black label society-bleed for me
amon amarth-the hero
slipknot- heritic anthem (all of slipknot's music)
dio-master of the moon

[Räserfräs]

Masterplan - Spirit never dies
Breaking Benjamin - Dance with the Devil
Cinder - Soul Creation
Hinder - How Long
Three Days Grace - Animal I have Become
Itchy Daze - Monster
Bullet for my Valentine - All these things I hate
Killswitch Engage - The end of Heartache
Dragonforce - Operation ground and pound
Pantera - F***ing Hostile

Not in order... just 10 songs i listen to quite often lately.... The list is looooong though!!! there are many kickass songs out there that easily could have smashed it's way in to this list! ^^

1. Blut Im Auge - Equilibruim
2. Friede sei mit dir - Die Apokalyptischen Reiter
3. Falling Apart - Zebrahead
4. Because of me - Seether
5. Inis Mona - Eluveitie
6. Down with the sun - Insomnium
7. Feuer Frei! - Rammstein
8. Clankiller - Wolfchant
9. Mourning Red - Wolfchant
10. I hate everything about you - Three Days Grace

[Rocket]

1. "I Hate Everything About You" - Three Days Grace
2. "Misery" - Green Day
3. "Your Love Is A Lie" - Simple Plan
4. "Mama" - My Chemical Romance
5. "Animal I Have Become" - Three Days Grace
6. "In The End" - Linkin Park
7. "Blood" - My Chemical Romance
8. "God Must Hate Me" - Simple Plan
9. "Crawling" - Linkin Park
10. "High School Never Ends" - Bowling For Soup

[earthbound]

i ddnt arrange them in order or anything
1-3 libras by perfect circle
2-god put a smile upon your face by coldplay
3-you and me and the devil makes 3 by marylin manson
4-overburned by disturbed
5-stricken by disturbed
6-the outsider by perfect circle
7-blue by perfect circle
8-droppin plates,disturbed
9-pet-perfect circle
10-devour by disturbed

hope u like