I know many people contributed to the idea of the elder beings that so populated Lovecraft’s ‘world’. Is there any way to find out, for instance, should I want to write a book with some of the things man was not meant to know, what beings I can use, and what I should avoid, to avoid stepping on someone else’s tentacles at a legal level?
(Wow, that was a long run-on sentance!)
In basic, is there a way to find out what is currently legally ‘owned’ of the elder things?
Nitpick- You say Elder Gods in the title, and elder things in your closing sentence. The two are not interchangable.
Actual Answer- After Lovecraft’s death, the cppyright to his works and the trademarks to stuff therein were left to relatives, then claimed by August Derleth. He grabbed a bunch of other stuff (whether he ever had legal right to do so is uncertain) and founded Arkham House to publish it. These days, many of the copyrights on Lovecraft, and the rest have expired. However, Chaosimum Inc currently owns trademark on Cthulhu, Yog Sothoth, etc and the distinctive likenesses thereof.
Some twenty or so years ago TSR included a Cthulhu Mythos section in their Deities And Demigods book. Chaosium made them cease and desist. Toy Vault is currently making plush Cthulhu Mythos toys under license from Chaosium. Chaosium continues to publish books, make t shirts etc.
IMO A work distributed for free, and with an acknowledgement that Shub Niggaurath etc are the trademarks of Chaosium would probably be ignored. Any work sold for profit is a clear trademark infringement and if Chaosium notices you, they shall unleash their lawyers. Note that although Mike Mignola’s work is filled with incredibly-thinly-veiled things from the Cthulhu Mythos, he never uses the original trademarked names.
You’re kidding. You can get a cuddly stuffed Cthulhu?
Yes you can. This is way too cool, now I know what to get my brother for Xmas! The Santa one is PERFECT.
The loophole is that you aren’t supposed to refer to the Elder Gods by name so…
I want the plush Nyarlethotep!
I have it bookmarked.
[Isn’t there some disupute over whether Arkham Publishing really has the rights to Lovecraft’s works? I mean, Lovecraft died in 1937 and it’s possible that nobody jumped the the loopholes required to extend the copyright.
Marc
And is there any way to know what I can put down on a page without Chaosium unleashing the killer lawers that shoot bees out of their mouth?
(And I happen to have two plush cthulhus on my sofa!) 
I read Browning’s Resume with Monsters and it makes repeated reference to Azathoth. I’m not sure if writing a novel using a name is the same thing as other uses of that name. Especially since Lovecraft encouraged other writers to use his gods, thus creating a widespread mythos. For instance, I’m pretty sure Tsathogguah wasn’t a Lovecraft creation.
As for the confusion in the OP, let’s review:
Elder Gods: Pretty much humanoid gods of the Dreamlands. Abducted Barzai the Wise of Mt. Kadiphonek.
Outer Gods: Odd, mindless hyper-powerful things like Azathoth. Nyarlathotep is their soul and messenger.
Elder Things: Intelligent, pentalaterally symmetrical creatures who lived on Earth long ago.
Great Old Ones: Scary things like Great Cthulhu, Yig, or Tsathogguah.
(I’m doing this from memory, so my apologies if that’s not perfectly accurate)
Copyright on Lovecraft’s work has definitely lapsed. Anybody who wants to can reproduce his works. However, Chaosium still holds trademarks on pretty much everything in the Cthulhu mythos.
Re Tsathogguah
Last time I checked, Chaosium also held trademark on those parts of the Cthulhu Mythos created by Frank Belknap Long, August Derleth, Clark Ashton Smith, Robert E Howard, etc.
Maybe this is a question best left to General Questions, but how can they trademark Cthulhu or anything else written by Lovecraft? Is this just a case of them being able to get away with it until someone challenges them in court?
Marc
So … lemme get this straight. I caN trademark characters, etc., from existing works of art whose copyrights have lapsed, and then I have the right to legally supress the sale of any work for profit that uses those characters? If I trademark Dracula I can force anyone who wants to sell a Dracula ANYTHING to get a license from me first?
I see whole new vistas opening up before me …
AFAIK The trademarks were grabbed by Derleth, some legitimately others not. He incorporated into Arkham House. Chaosium bought the trademarks from Arkham house. There’s a similar situation with Marvelman/Miracleman. We know who the legitimate right holders are now, and we can trace that back two steps. Then, it becomes unclear whether transfers were legitimate or if the property itself was such a blatant infringement as to be invalid in the first place.
You haven’t really addressed my question. It sounds like Arkham House has trademarked characters in works that are no longer in copyright. If this is the case, what’s to keep various entities from trademarking characters, etc., from various classic works that are long since out of copyright and essentially preventing anyone else from publishing or using the original characters?
August Derleth was Lovecraft’s friend and contemporary. Derleth’s claiming of trademarks and copyrights happened well before the copyrights expired.
So… Wait… I can, or can’t write about the great old ones? Or can I just not use specific names? Color me (out of space) confused. 
My guess is: you can write about them, but if you use their specific names, Chaosium will probably sue you for doing so if your work has any financial potential, maybe even if not. Chaosium may or may not having standing to sue you. Many companies use essentially frivolous lawsuits as a way of keeping less well-funded individuals and firms from competing effectively, since it costs money to defend yourself up front whether the lawsuit is deemed frivolous or not. Just another way the law serves the wealthy in America.