This should be fairly obvious, but anything actually from Tolkien's book and world can be discussed here, from The Hobbit to The Children of Hurin. The major requirement is it comes from Tolkien's works themselves, not from someone's else's version of them
That's not to say you can't, for example, compare Faramir's depiction in Peter Jackson's movies to Faramir as he was shown in the books. Discussing the finer points of a parody version of Sauron, however, would best be put in the "Misc Tolkien" board.
Sometimes it can be a fine line and I don't want to be harder about this than needs be. If there really is a legitimate question about whether it belongs here or not, you can post it and if it doesn't go here someone will say something and/or I'll move it myself. Chances are though that if the source material (LotR, Sil, Hobbit, etc) doesn't come into play in the discussion, it would be better put elsewhere.
"There Iluvatar permitted the Valar to maintain upon the Earth an abiding place, a memorial of that which might have been if Morgoth had not cast his shadow upon the world." -Akallabeth, The Silmarillion
"When you can do what you want, you will be who you are." -John Hagee (first person I heard use it anyway)