"I'm Haruhi Suzumiya, from East Junior High. First off, I'm not interested in ordinary people. But, if any of you are aliens, time-travelers, or espers, please come see me. That is all!" -Haruhi introducing herself.
"That's classified information." -Mikuru Asahina.
"..." -Yuki Nagato.
"I don't know how I know, I just know that I know, y'know?" -Itsuki Koizumi.
"Yare yare" -Kyon. Also Sasaki.
"Consider this if you will. You have a very unhappy person living in a certain place. Then, he opens his eyes one day, and the whole world is completely changed. It's a beautiful world. Calling it utopia doesn't do it justice, it's that wonderful. And this person will never be unhappy ever again. Over night, he was snatched from the jaws of Hell and taken straight to Heaven. The thing is, this person didn't do this himself. In fact, he had no idea who was responsible for changing his world. It was a total mystery. And that's how he stayed, never knowing who it was or why they did it, forever. So I ask you, is this something this person should be happy about?" -Kyon.
"Kyon-kun, denwa." ("Kyon-kun, [your] phone.) -Kyon's (unnamed) sister at the beginning of all of the Endless Eight episodes.
"We have entered an endless recursion in time." -approximately translated line from the same episodes that—along with the rest of the Endless Eight episodes—has become Memetic Mutation.