Music, ultimately. Movies, Mind Rotting Video Games, Nature, Technology, Religion, Science (all ranging from Astronomy, Biology, Physics, and Chemistry), Literature, Art-old and new, Violence, Obscenity, Macabre, Mythology, Ancient History, Drums, Drumming, Drummers, Writing, Animation, Skulls, Barcodes, Alchohol, Mind-altering Drugs, Psychological Phenomenon, Paranormality, Sociology, War, Politics, Etc. I think this is long enough.
Intelligent human beings.
GRINDCORE, Black Metal, Death Metal, Drum and Bass, Jungle, Doom Metal, Gore Metal, Viking Metal, Folk Metal, Power Metal, Classical, Classic Rock, Some Hair Metal, Goth Metal, Little Rap and Techno as well:1349, Abigor, Aborted, Abgott, Accept, AC/DC, Adorned Brood, Alice Cooper, Alice In Chains, Agathacoles, Amon Amarth, ANAL CUNT, Arch Enemy, Ashen Light, Athiest, Atreyu, Bal Sagoth, Bathory, Behemoth, Belphegor, the Berzerker, Beethoven, Between the Buried And Me, Black Label Society, Black Sabbath, Bloodbath, Burzum, Buddy Rich (Mostly Just Drum Solo's), Cannibal Corpse, Carcass, Carnal Forge, Carpathian Forest, Celtic Frost, Cephalic Carnage, Cephalotripsy, Cliteater, Charon, Children Of Bodom, Cradle Of Filth (Old), Crimson Death, (Early) CRYPTOPSY, Cynic, Danzig, Dark Funeral, Dark Tranquillity, Darkthrone, Death, Decapitated, Decrepit Birth, Def Leppard, (Early) Deftones , Deicide, Dimmu Borgir, Dio, Disgorge, Dismember, Disiples Of Power, Dragonlord, Drowning Pool, Dying Fetus, Einherjer, Elfsword, Emperor, Entombed, Exhumed, Faith No More, E.T.T.S., Fear Factory, FECAL CORPSE, Finntroll, Fuck...I'm Dead, Gaahlskagg, Gorgoroth, Gorguts, the Haunted, Hatebreed, Hypocrisy, Iced Earth, Immortal, I Mother Earth, I Shit On Your Face, Imeptigo, Iniquity, In Thy Dreams, Iron Maiden, Jack Off Jill, Job For A Cowboy, Judas Priest, Kittie, Korn, KRONOSFEAR, Lamb Of God, Led Zeppelin, Lord Gore, Maledictive Pigs, Malevolent Creation, Manowar, Marduk, (Some) Marilyn Manson, Martyr, Mastodon, Mayhem, Megadeth, Meat Shits, Metallica, Misery Index, Moonspell, Morbid Angel, Mortician, Motorhead, Mozart, Mudvayne (Old), Murderdolls, Nailbomb, Napalm Death, Nasum, Nazgul, Necrophagist, NEFARIOUS BAPTISM, Nerthus, Nevermore, New Order, Nightwish, Nile, Nine Inch Nails, Nirvana, Norther, Nothingface, Obituary, Obtained Enslavement, Old Man's Child, Opeth, Orgy, Otep, Ozzy Osbourne, (Some) Pantera, Pink Floyd, Possessed, Powerman 5000, Primordial, Psycroptic, Putrid Pile, Queens Of The Stone Age, Rage Against The Machine, Rammstein, Rigorous Obliteration, Rompeprop, Rotting Christ, Satyricon, Sentenced, Sepultura, Shadows Fall, SKINLESS, Slayer, Sleep Terror, Slipknot, Smashing Pumpkins, Spawn of Possession, Static-X, Strapping Young Lad, Suffocation, Superjoint Ritual, Svarrogh, System Of A Down (Old), Tanzwut, The Doors, Three Inches Of Blood, Thronde, Tim Curry, Tool, Trelldom, Troll, TYPE O NEGATIVE, Urinefestival, Visceral Bleeding, Vivaldi, Venom, Waking The Cadaver, White Zombie, Windir, Wintersun, (Some) Weezer, Zyklon, Zyklon-B
Lots of movies...Fight Club, Jay and Silent Bob Series, Jason movies, Freddy movies, Pumpkinhead, Garden State, Beetlejuice, Denis Leary, Brainstorm, Batman, Family Guy, Sin City, Alien, Predator, AVP, Matrix, Night Of The Living Dead, Nosferatu, House On Haunted Hill, Hellraiser, Resident Evil, 40 Year Old Virgin, Major Payne, Happy Gilmore, Mr. Deeds, Deuce Bigalow...so many more that remain unmentioned...
Family Guy, CSI (Las Vegas), Mindfreak, How It's Made, Ultimate 10..., Futurama, Spawn, Mission Hill, The Oblongs, Gilmore Girls, MuchLOUD, Enterprise, Spongebob Squarepants, Wrong Coast...etc
The Hobbit, LOTR, The Dark Half (S.King), Demon Seed (D.Koontz), Necroscope Series (B.Lumley), Anything By Anne Rice, The Call Of Cthulhu (Lovecraft), Anything Else By Lovecraft, Astronomy Books, Pornography...
Too many to list.