[Galadriel55]

About all the quotes that really shake me are put up already. I'll just add a few; I don't have the books on me right now, so I'll paraphrase:

...But the seeds of lie, planted by Morgoth, will continue to grow and bring crops...
(end of the Silmarillion)

Oh twice beloved! A Turin Turambar, turun ambarthanen! (oh Turin, Concouror of Fate, by fate concoured!)
(Nienor Niniel's words to Turin before juping into Teiglin)

Galadriel's description of what she will be if Frodo gave her the Ring, and the last sentence: "I've made my choice. I shall sail over the Sea and remain Galadriel"

Thus, I have fulfilled my oath.
(Finrod, when saving Beren, just before death)

And at that time there was no grief grated than the grief of the maia Melian
(when Melian discovers that Luthien became mortal)

I will not say, do not cry, for not all tears are for evil.
(Gandalf's last words in ME)

this one is more comic, than serious, but I like it nevertheless:
Do not ever laugh at a live dragon!
(Bilbo's thoughts after his dialogue with Smaug)



That is a lot! And I would include into my list most of the quotes that were already mentioned! To tell you the truth, I think that there is no unimportant line in any of Tolkien's books, even though some are more significant or evident than others.