I Am Legend and Animal Farm are two of my favorites.
For good Stephen King endings, I’d include 'Salem’s Lot and Desperation. And of course, most of his short stories.
Wild Seed by Octavia Butler. Emotionally very powerful.
On Stranger Tides by Tim Powers. Mostly because of the Epilogue, which is nothing like any epilogue ever written.
The Sot-Weed Factor by John Barth, simply because the revelation of the McGuffin is so perfect – hilarious and bawdy, and evidently something that was actually done. The final scene also is perfect.
Just want to say that I brought this game up after work last night, and the consensus winner so far is “Goodnight Moon”. Someone this morning sent out a quickly MS Paint version of this picture in this scene.
One Flew Over the Cuckoo’s Nest has a marvelous ending.
I like the final paragraph/sentence of Kerouac’s On The Road.
Thanks. I was trying to remember which book this was from. Great ending!
That, sir, is one bully ending.
For being an unfinished novel, The Trial packs a hell of a wallop at the end - “It was as though the shame of it should outlive him.”
The ending of My Gun is Quick by Mickey Spillane is the ultimate hard-boiled, ultra-violent ending, and I can quote it from memory.
It’s like cheap wine - raw, and with no pretensions to culture - but a helluva kick nonetheless.
Regards,
Shodan
1984 is the only one that I can just quote off the top of my head. That one felt like a punch to the gut, and I loved it when I first read it (on a plane to Maui in 1998 at the age of 14).
War for the Oaks by Emma Bull has a good ending, too.
They win the concert contest, the main characters kiss, and the battle’s won. And the book ends right after that; no coda, no anything. Just this awesome rush of a high point. Roll credits. Brilliant.
Okay, I just made fun of Stephen King in the other thread, so this answer makes me a big old hypocrite.
The Long Walk by Richard Bachman has one of my favorite endings ever. The absolute definition of a Pyrrhic victory.
Obvious from my user name that I think LOTR had a pretty damn good ending.
Also One Hundred Years of Solitude has a great beginning AND a great ending.
For Whom the Bell Tolls has an exquisite, perfect ending. The whole book is perfect.
Do short stories count? I’d like to share the ending of my all-time favorite short story, “The Last Question,” by Isaac Asimov.
And AC [super-evolved hyper-intelligent entity] said, “LET THERE BE LIGHT!”
And there was light----
That ending absolutely floored me.
Tales of the Otori
Otori Takeo is prophesied to be killed by his son who was raised by his arch-enemy. He is once again on the verge of losing his beloved government of peace and justice to the warlords Arai Zenko and and Saga Hideki. When his son Kikuta Hisao is brought to kill him by Kikuta Akio, he cannot do it. So Otori Takeo, on his beloved wife’s orders takes Hisao’s knife and plunges it into his belly taking his own life. But this is only after he has secured his legacy through his daughter, who has proved to the Shogun Saga Hideki that she deserves to inherit and rule the Three Countries. Otori Shigeko is promised to wed Saga Hideki, who now respects her because she has bested him in combat, twice, without killing him, by intention. Saga Hideki, and Otori Shigeko ride against the traitorous Arai Zenko, and put him down. Thus they secure the peace of the three countries as established by Otori Takeo fulfilling the grand dream of his adoptive Father, Otori Shigeru. Through Shigeko, the three countries remain, Otori.
Yes, this! The epilogue was just so perfect and heartbreaking.
Let’s not forget The Zombie Survival Guide! 
1984 by George Orwell
“He loved Big Brother.”
Made me throw up in my mouth when I read it the first time. Amazing.
Walter Jon Williams knows how to write some kick-ass endings. I love the endings he gave “Voice of the Whirlwind” and “Days of Atonement.”
The ending of Terry Pratchett’s Small Gods was a perfect ending to his best book.
A Storm of Swords, the third book of A Song of Ice and Fire by George R R Martin, ends with what feels like about 7 pieces of total asskicking in a row.
Sadly, book 4 wasn’t as good, and book 5 isn’t as existing.