I have provided a list of most of what I have heard in each of the following genres/groups. It serves as both a recommendation list for you and a list of what I have so that you will be better able to recommend me things that I haven't heard. Feel free to laugh at the patheticness of all the groups except for dm.
Death Metal (some is death/grind, some melodic, some melodeath, some death/thrash, some death/black, some death/doom, etc ):
Abhorrence (Bra)
Ablaze My Sorrow
Aborted
Abramelin
Adramelech
Afflicted
Amon Amarth
Amorphis
Anasarca
Anata
Ancient Necropsy
Appalling Spawn
Arch Enemy
Arghoslent
Arsis
Asgard (Fra)
Asphyx
At the Gates
Atheist
Atrocity (Ger)
Autopsy
Autumnblaze
Autumn Leaves
Baal (Mex)
Banished (US)
Baphomet (US)
Beheaded (Mlt)
Behemoth (Pol)
Blood Red Throne
Bloodbath (Swe)
Bolt Thrower
Brodequin
Brutality
Brutus (Hol)
Burden of Grief
Cadaver
Capharnaum
Carbonized (Swe)
Carcass
Carnage (Swe)
Cemetary
Cenotaph (Mex)
Ceremonial Oath
Ceremonium
Ceremony (Hol)
Chastisement
Cianide
Cinerary
Coffin Texts
Convulse
Creepmime
Crematory (Swe)
Crimson Thorn
Crypt of Kerberos
Cryptopsy
Cynic (US)
Dark Tranquillity
Daylight Dies
Death
Debodified
Decapitated (Pol)
Decrepit Birth
Deeds of Flesh
Dehumanized
Deicide
Delirium (Hol)
Demigod (Fin)
Demilich
Demonoid
Depresy
Deteriorot
Disarmonia Mundi
Disavowed
Disillusion
Disincarnate
Dismember
Domination Through Impurity
Drawn and Quartered
Edge of Sanity
Embracing
Engorged
Entombed
Epoch of Unlight
Estuary
Eternal Darkness (Swe)
Eternal Lies
Eternal Tears of Sorrow
Eucharist
Excruciate (Swe)
Facebreaker
Farmakon
Fester (Nor)
Fleshcrawl
Fleshless
Forgotten Silence
Fragments of Unbecoming
Funebre (Fin)
Garden of Shadows
Gardenian
Gates of Ishtar
God Among Insects
God Macabre
Golem (Ger)
Gorement
Gorgasm (US)
Gorguts
Gory Blister
Grave
Greenfly
Harakiri
Hollenthon
Holymarsh
Hypnös
Hypocrite
Illogicist
Immersed in Blood
Immolation
Impaled
In Flames
In Ruins
In-quest
Incantation
Infester
Infliction (US)
Insision
Insomnium
Internal Decay
Intestine Baalism
Inverted
Julie Laughs Nomore
Kaamos (Swe)
Krisiun
Kronos
Lemming Project
Liers in Wait
Lucifer
Luciferion
Lust of Decay
Lykathea Aflame
Man Must Die
Martyr (Can)
Massacra
Massacre (US)
Mercenary (Dnk)
Miasma
Mithras
Molested
Monstrosity (US)
Moonshine
Morbid Angel
Morpheus Descends
Mortal Decay
Mortuary (Mex)
Mythic
Necrophagist
Necrophobic (Swe)
Nightrage
Nile
Nocturnus
Nonexist
Obtruncation
October Tide
Old Funeral
Ominous (Swe)
Omnium Gatherum (Fin)
Opeth
Ophiolatry
Order From Chaos
Origin
Pestilence
Phlebotomized
Poppy Seed Grinder
Possessed
Psycroptic
Psypheria
Pungent Stench
Pyaemia
Pyrexia
Quo Vadis (Can)
Repulsion
Revenant (US)
Ribspreader
Sacramentum
Sacrilege (Swe)
Saprogenic
Sarcasm (Swe)
Sauron (US)
Scythe (Ger)
Seance (Swe)
Sepsism
Serpens Aeon
Severe Torture
Severed Savior
Shadow
Sickening Horror
Silent Stream of Godless Elegy
Sinister (Hol)
Sinners Bleed
Sleep Terror
Soilwork
Sorcery (Swe)
Spawn (Ger)
Spawn of Possession
Suffer (Swe)
Suffocation (US)
Suidakra
Summer Dying
Terrorizer
The Black Dahlia Murder
The Chasm
The Circle of Zaphyan
The Embraced
The Fifth Sun
Theory in Practice
Therion (Swe)
Torchure
Torture Squad
Unanimated
Uncanny (Swe)
Unleashed (Swe)
Unmoored
Urkraft
Utumno (Swe)
Vader
Vastion
Vehemence
Vile (US)
Visceral Bleeding (Swe)
Vital Remains
Vomit Remnants
Vomitory (Swe)
Vore
Wicked Innocence
Withered Beauty
Within Y
Wombbath
Wormed
Black Metal/Folk/Viking:
...And Oceans
1349
Absu
Abysmal
Abyssic Hate
Aeternus
Agalloch
Arcturus
Ásmegin
Beherit
Blut Aus Nord
Burzum
Countess
Damnation (Swe)
Darkestrah
Darkmoon
Darkthrone
Darkthule
Dawn (Swe)
Deathspell Omega
Deströyer 666
Dimmu Borgir
Dissection (Swe)
Drudkh
Emperor
Empyrium
Enslaved
Falkenbach
Finntroll
Funeral Mist
Gontyna Kry
Grand Belial's Key
Ikuinen Kaamos
Imperial Crystalline Entombment
Immortal
Judas Iscariot
Krohm
Leviathan (US)
Marblebog
Megiddo (Can)
Mithotyn
Mjölnir (Ger)
Moonblood
Mysticum
Naglfar (Swe)
Nargaroth
Nest
Noenum
Nokturnal Mortum
Oathean
Old Man's Child
Primordial
Rivendell
Sad Legend
Samael
Satan's Blood
Sort Vokter
Sturmgeist
Summoning
Tearstained
The Eye
Trollech
Ulver
Velvet Cacoon
Venom
Vinterriket
Watain
Weakling
Windir
Winter of Apokalypse
Wintersun
Woods of Ypres
Xasthur (US)
Power/Folk/Prog:
Age of Silence
Alarum
Andromeda (Swe)
Blind Guardian
Children of Bodom
Communic
Dragonforce
Dream Theater
Equilibrium (Ger)
Iron Maiden
Kalmah
Orphaned Land
Pain of Salvation
Wuthering Heights
Doom/Sludge:
Arcane Sun
Crowbar
Cult of Luna
Doomsword
Down
Esoteric
Evoken
Katatonia
Morgion
Mourning Beloveth
Nightrealm (Fin)
Nortt
Novembers Doom
Novembre
Pelican
Rapture (Fin)
Skepticism
Slumber (Swe)
Solitude Aeturnus
Swallow the Sun
The 3rd and the Mortal
Thergothon
Tiamat
Void of Silence
Thrash:
Coroner
Dark Angel (US)
Dekapitator
Exodus
Hypnosia
Iced Earth
Kreator
Megadeth
Metallica
Morbid Saint
Slayer (US)
Death Metal (some is death/grind, some melodic, some melodeath, some death/thrash, some death/black, some death/doom, etc ):
Abhorrence (Bra)
Ablaze My Sorrow
Aborted
Abramelin
Adramelech
Afflicted
Amon Amarth
Amorphis
Anasarca
Anata
Ancient Necropsy
Appalling Spawn
Arch Enemy
Arghoslent
Arsis
Asgard (Fra)
Asphyx
At the Gates
Atheist
Atrocity (Ger)
Autopsy
Autumnblaze
Autumn Leaves
Baal (Mex)
Banished (US)
Baphomet (US)
Beheaded (Mlt)
Behemoth (Pol)
Blood Red Throne
Bloodbath (Swe)
Bolt Thrower
Brodequin
Brutality
Brutus (Hol)
Burden of Grief
Cadaver
Capharnaum
Carbonized (Swe)
Carcass
Carnage (Swe)
Cemetary
Cenotaph (Mex)
Ceremonial Oath
Ceremonium
Ceremony (Hol)
Chastisement
Cianide
Cinerary
Coffin Texts
Convulse
Creepmime
Crematory (Swe)
Crimson Thorn
Crypt of Kerberos
Cryptopsy
Cynic (US)
Dark Tranquillity
Daylight Dies
Death
Debodified
Decapitated (Pol)
Decrepit Birth
Deeds of Flesh
Dehumanized
Deicide
Delirium (Hol)
Demigod (Fin)
Demilich
Demonoid
Depresy
Deteriorot
Disarmonia Mundi
Disavowed
Disillusion
Disincarnate
Dismember
Domination Through Impurity
Drawn and Quartered
Edge of Sanity
Embracing
Engorged
Entombed
Epoch of Unlight
Estuary
Eternal Darkness (Swe)
Eternal Lies
Eternal Tears of Sorrow
Eucharist
Excruciate (Swe)
Facebreaker
Farmakon
Fester (Nor)
Fleshcrawl
Fleshless
Forgotten Silence
Fragments of Unbecoming
Funebre (Fin)
Garden of Shadows
Gardenian
Gates of Ishtar
God Among Insects
God Macabre
Golem (Ger)
Gorement
Gorgasm (US)
Gorguts
Gory Blister
Grave
Greenfly
Harakiri
Hollenthon
Holymarsh
Hypnös
Hypocrite
Illogicist
Immersed in Blood
Immolation
Impaled
In Flames
In Ruins
In-quest
Incantation
Infester
Infliction (US)
Insision
Insomnium
Internal Decay
Intestine Baalism
Inverted
Julie Laughs Nomore
Kaamos (Swe)
Krisiun
Kronos
Lemming Project
Liers in Wait
Lucifer
Luciferion
Lust of Decay
Lykathea Aflame
Man Must Die
Martyr (Can)
Massacra
Massacre (US)
Mercenary (Dnk)
Miasma
Mithras
Molested
Monstrosity (US)
Moonshine
Morbid Angel
Morpheus Descends
Mortal Decay
Mortuary (Mex)
Mythic
Necrophagist
Necrophobic (Swe)
Nightrage
Nile
Nocturnus
Nonexist
Obtruncation
October Tide
Old Funeral
Ominous (Swe)
Omnium Gatherum (Fin)
Opeth
Ophiolatry
Order From Chaos
Origin
Pestilence
Phlebotomized
Poppy Seed Grinder
Possessed
Psycroptic
Psypheria
Pungent Stench
Pyaemia
Pyrexia
Quo Vadis (Can)
Repulsion
Revenant (US)
Ribspreader
Sacramentum
Sacrilege (Swe)
Saprogenic
Sarcasm (Swe)
Sauron (US)
Scythe (Ger)
Seance (Swe)
Sepsism
Serpens Aeon
Severe Torture
Severed Savior
Shadow
Sickening Horror
Silent Stream of Godless Elegy
Sinister (Hol)
Sinners Bleed
Sleep Terror
Soilwork
Sorcery (Swe)
Spawn (Ger)
Spawn of Possession
Suffer (Swe)
Suffocation (US)
Suidakra
Summer Dying
Terrorizer
The Black Dahlia Murder
The Chasm
The Circle of Zaphyan
The Embraced
The Fifth Sun
Theory in Practice
Therion (Swe)
Torchure
Torture Squad
Unanimated
Uncanny (Swe)
Unleashed (Swe)
Unmoored
Urkraft
Utumno (Swe)
Vader
Vastion
Vehemence
Vile (US)
Visceral Bleeding (Swe)
Vital Remains
Vomit Remnants
Vomitory (Swe)
Vore
Wicked Innocence
Withered Beauty
Within Y
Wombbath
Wormed
Black Metal/Folk/Viking:
...And Oceans
1349
Absu
Abysmal
Abyssic Hate
Aeternus
Agalloch
Arcturus
Ásmegin
Beherit
Blut Aus Nord
Burzum
Countess
Damnation (Swe)
Darkestrah
Darkmoon
Darkthrone
Darkthule
Dawn (Swe)
Deathspell Omega
Deströyer 666
Dimmu Borgir
Dissection (Swe)
Drudkh
Emperor
Empyrium
Enslaved
Falkenbach
Finntroll
Funeral Mist
Gontyna Kry
Grand Belial's Key
Ikuinen Kaamos
Imperial Crystalline Entombment
Immortal
Judas Iscariot
Krohm
Leviathan (US)
Marblebog
Megiddo (Can)
Mithotyn
Mjölnir (Ger)
Moonblood
Mysticum
Naglfar (Swe)
Nargaroth
Nest
Noenum
Nokturnal Mortum
Oathean
Old Man's Child
Primordial
Rivendell
Sad Legend
Samael
Satan's Blood
Sort Vokter
Sturmgeist
Summoning
Tearstained
The Eye
Trollech
Ulver
Velvet Cacoon
Venom
Vinterriket
Watain
Weakling
Windir
Winter of Apokalypse
Wintersun
Woods of Ypres
Xasthur (US)
Power/Folk/Prog:
Age of Silence
Alarum
Andromeda (Swe)
Blind Guardian
Children of Bodom
Communic
Dragonforce
Dream Theater
Equilibrium (Ger)
Iron Maiden
Kalmah
Orphaned Land
Pain of Salvation
Wuthering Heights
Doom/Sludge:
Arcane Sun
Crowbar
Cult of Luna
Doomsword
Down
Esoteric
Evoken
Katatonia
Morgion
Mourning Beloveth
Nightrealm (Fin)
Nortt
Novembers Doom
Novembre
Pelican
Rapture (Fin)
Skepticism
Slumber (Swe)
Solitude Aeturnus
Swallow the Sun
The 3rd and the Mortal
Thergothon
Tiamat
Void of Silence
Thrash:
Coroner
Dark Angel (US)
Dekapitator
Exodus
Hypnosia
Iced Earth
Kreator
Megadeth
Metallica
Morbid Saint
Slayer (US)