Itachi:
It is foolish to fear what we have yet to see and know!
People live their lives bound by what they accept as correct and true. That's how they define "reality". But what does it mean to be "correct" or "true"? Merely vague concepts… their "reality" may be nothing but an illusion. Can we consider them to simply be living in their own world, shaped by their beliefs?
Pain: We are both ordinary men, fighting for vengeance under the banner of justice. But if there is justice in vengeance, then justice will only breed more vengeance.
Hiruzen's poem about konoha

"When the tree leaves dance, one shall find flames. The fire's shadow will illuminate the village, and once again, tree leaves shall bud anew."
and also at the end of Kakashi gaiden, Hiruzen is talking at the end (in the anime)
Jiraiya when he was dying, one of the best speeches of the series. and the "Give up, on me giving up!" speech from tales of a gutsy ninja
and Kakashi's speech when Naruto defeated Kakuzu. both when he was talking about naruto to yamato, and also when he was talking to kakuzu before he finished him off.
edit: Shikaku's speeches to Shikamaru are always interesting too.