Villainous Breakdown: It's noted that when Sauron finally clicks to the fact that the heroes want to destroy the Ring rather than use it against him, he begins to feel utterly terrified.
Villains Want Mercy: Wormtongue begs for mercy when his plot with Saruman is discovered and defeated, claiming that he was working for the greater good of Rohan. He's allowed to live, a decision that costs quite a few lives and considerable grief.
Wacky Wayside Tribe: The whole Tom Bombadil episode almost certainly counts. Its arguable status as Padding, as well as its mixed reception among readers meant that it got skipped by The Movies.
A more literal example would be the Woses, led by Ghan-buri-Ghan. Also skipped by The Movies.
War Elephants: The Southrons ride to battle on "Oliphaunts" (as the hobbits call them) or mûmakil (as they're referred to by the Men of Gondor). Sam is very excited when he gets to see one at a distance — he and Frodo are now the only living hobbits ever to have seen a live Oliphaunt. (The others could have seen them at the Battle of the Pelennor Fields, but Pippin was too busy dealing with Faramir, Denethor, and Gandalf to bother watching from the walls of Minas Tirith, and Merry — having come with the Rohirrim — was too far to the west of the battlefield.)
War Refugees: Many in Rohan. In Gondor, Pippin arrives just in time to see them evacuated.
Warrior Poet: Applies to many characters, who are both capable fighters and cultured. The Elves are particularly brilliant at it, but the vast majority of the characters can and do improvise verses at the drop of a hat.
Special mention goes to Gimli, despite his gruff nature, whose long, blissful monologue on the caves of Helm's Deep is eloquent enough to convince Legolas, a Wood Elf, that stones have majesty to rival any forest. After Gimli actually takes him to see the caverns, Legolas admits that he is completely lost for words by comparison.
Warrior Prince: Most of the main characters, since the only major character not descending from a high (or at least respectable) bloodline is Samwise, whose ancestors always were just ordinary people — gardeners, ropemakers and such.
Weakened by the Light: A lot of Evil creatures, including orcs/goblins, trolls (turned to stone), the Nazgûl, Shelob and Gollum. Sauron manages to block out the sun before the assault on Minas Tirith, enabling his armies to fight at their full strength during the day.
We ARE Struggling Together: The elves, dwarves, and men are constantly squabbling with each other when they should be joining forces to fight the Evil Overlord. The Lothlórien elves distrust Gimli the dwarf, and so all the Fellowship must go blind into the path to Lórien:
"Alas for the folly of these days!" said Legolas. "Here all are enemies of the one Enemy, and yet I must walk blind, while the sun is merry in the woodland under leaves of gold!" "Folly it may seem," said Haldir. "Indeed in nothing is the power of the Dark Lord more clearly shown than in the estrangement that divides all those who still oppose him."
We Can Rule Together: Saruman pulls this on Gandalf. He turns down the offer and ends up being a prisoner.
Well-Intentioned Extremist: Boromir wants the One Ring to protect Gondor, and by extension the rest of the free world, but his eventual attempt to take it from Frodo doesn't gowell at all. This trope is also mentioned as how all good people who deliberately set out to wield the Ring will begin their unavoidable Start of Darkness: Both Gandalf and Galadriel say that if they wielded the Ring they would begin with doing good, but that's not how things would end as its evil power corrupts them.
Sauron started off as one, desiring to establish order in Middle-Earth, which decayed into a desire for tyranny. Tolkien portrays tyranny as the corrupted mockery of order just as chaos is the dark counterpart of freedom. Some tyrants just want power at any cost from the beginning; Sauron originally intended to use that power to create his own order, but kind of forgot it on the way. By the time of the book though all that was ancient history and he had evolved into something not far from an Omnicidal Maniac. "Nothing is truly evil in the beginning. Even Sauron was not so."
What Happened to the Mouse?: Painstakingly averted, to a point where even the fates of stolen ponies are usually accounted for in the narration.
Except, oddly enough, for Radagast the Brown. He shows up in a flashback, unwittingly directs Gandalf into the clutches of Saruman, and then never appears again. Someone mentions going to his house in the woods to try and find him, but the house has long been abandoned.
[Sam] wondered what the man's name was and where he came from; and if he was really evil of heart, or what lies or threats had led him on the long march from his home; and if he would rather have stayed there in peace...
What You Are in the Dark: Invoked by the Rangers, who intentionally stay out of sight to keep the threats they battle equally unknown to the simple people of Bree and The Shire.
When Trees Attack: Ents, Huorns, and Old Man Willow. Ents are ancient spirits which had grown tree-like in appearance after having been around them for thousands of years. Huorns are described as either "Tree-ish" Ents or "Ent-ish" trees, being less active than Ents but more awake than trees. They seem to be formed from Ents who had "gone to sleep" or trees which had "woken up". Old Man Willow, like most of what happens in the Tom Bombadil section, is never properly explained.
"Where Are They Now?" Epilogue: LotR did originally have one, which was cut for the original publication, but its three versions have since been published in the HoMe 9: Sauron Defeated. The first two versions are almost identical: It shows an evening seventeen years after the Ring's destruction, with Sam just having finished reading the story to his children, and answering their questions about the story and what happened after. The third version skips ahead a bit, and begins with Sam writing down the Q&A session with his children and talking to Elanor, who is allowed to stay up after the other children because she's oldest and it's her birthday. All versions end with a scene of Sam and his wife standing outside at night.
Also, the orcs whipping the hobbits to keep running (Merry and Pippin in The Two Towers on their run that ends in Fangorn Forest, and Frodo and Sam in The Return of the King, when they're mistaken for orcs in Mordor).
Who Wants to Live Forever? - Averted in most cases: the elves are innately immortal and - although rendered melancholy by the many things they've lost - seem to cope well enough. The same applies to the Ents (not immortal but spectacularly long-lived). The inhabitants of the Dwimorberg, however, definitely yearn for death, and there are signs of this attitude in Sméagol as well.
Wizards Live Longer: Justified with the "wizards" who are explained to be divine beings on the level of Biblical angels.
Played with in the Nazgûl . Their rings of power enhanced their lifespans far beyond that of ordinary mortals while simultaneously giving them magical powers, but the ultimate price was the loss of their souls, humanity, and free will to Sauron. In Middle-Earth, unless you're an elf or Physical God and therefore naturally immortal, prolonging your life always comes with a cost. (The one exception being the Kings of Númenor, whose lives got shorter the more evil they got - justified since their long lives were originally derived from their half-Elvish nature, which they were increasingly abandoning.)
The implication is that the mortals can't get any more life than they naturally have; they just spread it thinner and thinner, until they are little more than pseudo-living shadows.
Also, Éowyn's color of choice. She is also known as the White Lady of Rohan.
Woobie, Destroyer of Worlds: Invoked when Bilbo, Frodo, and finally Sam take pity on Gollum, ensuring the Ring's destruction. Gollum (and Frodo) practically become this, however.
This mainly applies to Gollum, since the Ring would have prevented the actual bearer from throwing it in, regardless of motivation, as he actively tried to prevent the Ring's destruction after centuries of misery and torment, because of a Heel Face Door Slam...
Although he was destined to destroy the Ring and so the quest would have failed without his attempt to prevent it. Literally Bilbo, Frodo and Sam taking pity on him was necessary for the Ring's destruction; and expressly choosing not to attack and kill him on four separate occasions, including on the slopes of Mount Doom.note According to Word of God, Gollum's only other option was to steal the Ring and throw himself in, or for the Ringbearer to throw himself in, or (had Aragorn been with them) to throw the Ringbearer in or claim the ring themselves. And there is speculation that the Voice of the Ring itself doomed the Ring when Frodo prophesied Gollum's death while wielding the Ring to control Gollum (one of only two times he does so) on the slopes of Mount Doom.
Frodo: But do you remember Gandalf's words: Even Gollum may have something yet to do? But for him, Sam, I could not have destroyed the Ring. The Quest would have been in vain, even at the bitter end. So let us forgive him! For the Quest is achieved and now all is over. I am glad you are here with me. Here at the end of all things, Sam.
Words Can Break My Bones: The basis of what we call magic in the setting. Spells are just that, words or snatches of verse or song that have inherent power. Names are also important, as are vows and promises made.
Peace and healing are way better than war and fighting. When Faramir (who is, granted, a Gondorian, but also the closest thing to an Author Avatar) directly compares Gondor and Rohan, he characterizes Rohan as less wise and advanced because they happily embrace the Proud Warrior Race Guy ethos and enjoy battle for its own sake. Gondor only slid into it out of necessity after being Proud Scholar Race Guys. Beregond later laments that Faramir is less admired than Boromir because he's scholarly and only kills at need, rather than a Glory Seeker, as though being smart and being brave are mutually exclusive.
Eowyn, a Glory Seeker and Death Seeker, doesn't find happiness in war (in part because she survives it, very much not her intent). Instead she finds it with Faramir, who as mentioned above, is a big player in the "peace is better than war" theme and decides that she's going to dedicate herself to healing, not the sword.
You Can't Fight Fate: Actually done in a positive way. Gandalf reassures Frodo by saying that Bilbo was meant to find the ring and Frodo was meant to have it, which is an encouraging thought. (Taken in the full context of the Legendarium, it's possible that he meant God was quietly nudging things in favor of the good guys.)