I have a whole lot of links in my research folders. Here are a few that might be useful for Supernatural or other fanfic writing.
Ghosts
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Haunted Places: sorted by state, also has international pages.
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Wikipedia's List of Unusual Deaths: Many notably atypical deaths throughout history, any of which could be co-opted or adapted for a ghost's origin story. These are all deaths of real people though, and many are quite disturbing. O.o
Folklore and Urban Legends
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American Folklore: Good site for lots of North American tales and folklore, ghost stories, some of the more common Urban Legends.
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Folktexts: From Aesop's fables to variations on classic 'fairy tales' to several folktales which have been used in Supernatural (Hand of Glory, Changelings, etc) and many more that would fit easily as a part of a case-fic, if you look through the list (two pages, alphabetized mostly by type) and sift. Keep in mind, these are from all through history, and many may be offensive by today's morals.
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More Urban legends at Warphead Cryptozoology (Sasquatch, lake monsters, wendigos, chupacabras, etc.)
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American Monsters-
Cryptozoo Books, texts, religion, spiritualism and so forth
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Esoteric Archives-
Sacred Texts Naming Characters
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Most popular baby names 1880 - 2005-
Kleimo Name generator: Based on census data. You can set how obscure you want a name to be. Good for generating lists of names of former victims, or suspects.
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Behind The Name: Lets you search first names by meaning, also subdivides into nationality.
Random stuff
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Weird town names and their origins-
Bizarre Holidays-
The Gobbler: A hotel Sam and Dean really really need to stay in at some point in their lives. Seriously, just look at the damn thing. Doesn't it scream for Winchester befuddlement?
This is about the sanest room it's got. Apparently it was torn down somewhere around 1997, but what the heck, maybe it's haunting whatever they built over top of the site, because you know decor like that will not die quietly. (Caution, site has autoplaying intro thing with sound. There's also a page here and there that plays the hotel's jingle with no warning, so best leave the sound turned waaaay down.)
Hope someone finds something interesting in all that! :-)