COH in its entirety.
The ending of
LOTR. I do find it ironic that Frodo goes through everything with the Shire in his mind, just to come back and find out that he cannot have it anymore.
Morgoth's loss in
The Sil. He pretty much provided good ground for his own destruction: if it wasn't for the destruction of BOTH Doriath and Gondolin, Earendil and Elwing would never have reached Valinor.
Sam's relationship to Gollum. Sam tries to help and protect Frodo. He is suspicious of Gollum, sometimes insulting him. If he wasn't so offensive, maybe it would help Frodo more in "taming" Gollum and bringing the Smeagol out of him. That almost happened (when Frodo was asleep and Gollum was reaching for him with a sad look) but Sam stopped it from happening, unconciously.
Starved "Fatty" Bolger. Need I explain?
Gorbag. "Orc philosopher" sounds more than a bit oxymoron-ic, doesn't it?
And related to that, "the great Elf warrior with a bright sword..." or some such. Also, that the orcs were afraid of him.
Pippin as Ernil i-Pheriannath. The most un-noble hobbit ever, who got this reputation only because he was with Gandalf and spoke with Denethor.
Bilbo finding the Ring. Call it fate, as Gandalf did, but it was still some situational irony on the Ring's part.