Since people are encouraged to create their stories here, I'd like to provide some things that can inspire good horror or creative antagonists/artefacts. Not everything on this list is horror, and many examples contain plenty of stuff that is against the rules. That's because it's inspiration - not copypaste material!
Stuff that costs money
Free Stuff
Things that are not colour-coded can be both, for instance a show can be watched on TV for free, but can also be rented or bought.
Shows
- Warehouse 13 (rarely creepy, but the concept of artefacts in this show can be translated very well into the Mirrorverse - especially when transferred to rituals. it also gives plenty of inspiration for how artefacts or cursed objects could work or be created)
- Supernatural (just try to be more of a Losechester than a Winchester ;D)
- Special Unit 2 (good inspiration for especially corporeal entities, even though the creepy needs to be cranked up quite a bit)
- Paranoia Agent (great inspiration for mental, delusion and dream based horror)
- Perfect Blue (very focused on what scares the individual)
- Medium (more so than "Ghostwhisperer", because "Medium" has more erratic, less comprehensible ghosts - and sometimes even entities that trick the eponymous medium, abusing and exploiting her clairvoyance)
- Doctor Who (The new series contains plenty of scream material)
Movies
- Paprika (again, excellent for dream and mind based horror)
- Room 1408 (good psychological horror)
- The Woman in Black
- Stephen King's Rose Red
- Pretty much every adaption of "Carrie"
- Most of the things on this list in general
- Poltergeist
- The Others
- Let the right one in (yes, romantic vampire movie - but good for its dark tone)
- Most movies by Roman Polanski
Games
- Bioshock
- Minecraft (Singleplayer Survival, especially on the hardest mode)
- F.E.A.R.
- Project Zero/Fatal Frame
- Portal II
- Mirai Nikki
- Ib
- Chzo Mythos Games
- Slender
- The SCP games (SCP-087, SCP-087-b, SCP Containment Breach)
Music
- The Portal soundtracks
- Likewise: The Bioshock soundtracks
Creepypastas
- The origin thread of Slender Man on SomethingAwful
- Everything on this list
- The Rake
- Smile Dog
- Jeff the Killer (I don't think it's that great, but it's included for fame)
- Candle Cove (excellent example!)
- In the Mirror
- The Girl in the Picture
- The Baby Doll
(I'll keep adding to this list with things you submit here)
Literature
- John dies at the End
- This Book is full of Spiders
- House of Leaves
- Coraline
- Everything H. P. Lovecraft ever wrote (Seriously - this man invented the horror genre as we know it! His short stories and letters are basically the first popular creepypastas.)
- Everything Edgar Allan Poe ever wrote
- Many works by Franz Kafka as well
- Less perfect, but still good inspiration are Stephen King and R. L. Stine ("Goosebumps" series)
- Once