Chaosium - Home page of company that publishes Call of Cthulhu.
Pagan Publishing - Publishers of many fine Call of Cthulhu products, including the outstanding Delta Green, The Unspeakable Oath magazine, and The Hills Rise Wild miniatures game.
Arc Dream - Publishers of the Godlike roleplaying game and Wild Talents, and co-publishers of Delta Green: Eyes Only and Delta Green: Targets of Opportunity. Godlike is a superhero roleplaying game set in World War II, written by Dennis Detwiller of Pagan Publishing and Greg Stoltz of Atlas Games. This site includes the free Cthulhulike download for converting Call of Cthulhu and Delta Green to Godlike's "One Roll Engine" (ORE) game system.
Atlas Games - Publishers of Over The Edge, Feng Shui, Cults Across America and Unknown Armies roleplaying game (co-written by Pagan Publishing's John Tynes).
Biohazard Games - Publishers of Killer Crosshairs, an excellent supplement for firearms combat.
Byakhee - A good freeware Call of Cthulhu character generation program.
Cthulhu Lives - Home of the H. P. Lovecraft Historical Society, a group of Cthulhu Live players. They also produce professional sounding musical CDs (like the A Very Scary Solstice CD of Cthulhu based Christmas carols), and provide free font and prop downloads.
Cthulhu Rising - Call of Cthulhu roleplaying in a dark future. This is the home, and the support site, for the Cthulhu Rising monograph published by Chaosium. The game offers Mythos adventures in a stereotypical science fiction background. It seems to ignore the Delta Green canon and the End Times prophesied in Lovecraft's work.
Delta Green - The official Delta Green web site. It contains excellent campaign materials within The Ice Cave.
Propping Up The Mythos - Creating Cthulhu Mythos props for fun and gaming.
Shoggoth.net - An interactive forum for the "cthulhu mythos community". It contains news and posts pertaining to the Cthulhu mythos in general and the Call of Cthulhu roleplaying game in particular.
Tales of Terror - Scenario ideas for Call of Cthulhu.
Toxic Bag Productions - Makers of roleplaying special effect CDs.
The Complete Works of H. P. Lovecraft - An excellent online collection of H. P. Lovecraft's writings.
Cthulhu, Where Are You? - The Scooby Doo expansion for the Mythos, the Call of Cthulhu collectible card game.
Darkets of the Hillside Thickets - A Vancouver based band that does Cthulhu Mythos inspired music.
Fortean Times - The official web site of the news stand magazine of the truly weird. Lots of great scenario ideas in each issue.
Jazz Age Slang - A listing of 1920s slang.
The H. P. Lovecraft Archive - A site describing Lovecraft and his writings, including non-fiction writings.
Miskatonic University - The home page of Arkham, Massachusetts very own Miskatonic University. Go Pods!
Mythku - Home of the Cthulhu Mythos haiku.
Mythos Online - An online bi-monthly Cthulhu Mythos e-zine.
Reader's Guide to the Cthulhu Mythos - The name says it all...
Yogsothoth.com - An excellent Call of Cthulhu support site. This is the home of the Call of Cthulhu player location list, which is how I met the people in my current gaming group. (Note the hyphen in the URL, otherwise you will end up at another site.)