Call of Cthulhu
Chuckling Cthulhu, Cthulhu Live, Cthulhu Lives - the HP Lovecraft Historical Societ, PST Productions, Werebadger - Cthulhu/Lovecraftian LARPs, Wraith
World of Darkness
Camarilla, Characters, Chronicles, Mailing Lists, One World by Night, Web Rings, Alex's Mostly Vampire Page, Beginners Guide to Vampire: Requiem, Duke's Haven, Gangrel Forest, Grapevine LARP Administration Utility, Look before you LARP, Morgantown by Gaslight, Rough Cut's Resources for LARPers, Software for Storytellers, Vampire Character Generator
Beyond Reality LARP
A Missouri-based group which runs modern horror games at conventions. Uses it's own d20 system and setting.
Fear of the Dark
Specializes in organising and running horror and murder/mystery events. All events are catered and insurance is included. Located in the United Kingdom.
In Nomine LARP
Austin, Texas game based on Steve Jackson Games' tabletop game of angel/demon conflicts.
Midnight's Children: Dark Theatres of the Min
A post-apocalyptic supernatural LARP set in California, but played in Toledo, Ohio.
Subterranean Homesick Games
Authors of live action games, in the interactive literature style. Site contains information on each of the stories they have created.
The Company of Crimson
Campaign information for a gothic horror LARP set in Victorian England
The Loom
Rules and game mechanics for vampire LARP gaming in the Pandemonium world. Located in California, United States.