All-time greatest Joker moment:

The Joker: What's the matter, Batman? No witty comeback? No threat? Then I'll provide the narration...
the screen flickers to life and "Our Home Movies" appears
The Joker: I'll begin with how I peeled back the layers of the boy's mind. Oh, he bravely tried to fight it at first. You would've been proud to see him so strong.
on the screen, the home video of Joker electrocuting Robin appears
The Joker: But all too soon, the shocks and the serums took their toll, and the boy began to share such secrets with me. Secrets that are mine alone to know... Bruce. It's true, Batsy! I know everything. And kinda like the kid who peeks at his Christmas presents, I must admit, it's sadly anti-climactic. Behind all the sturm and bat-o-rangs, you're just a little boy in a playsuit, crying for mommy and daddy! It'd be funny if it weren't so pathetic.
pause
The Joker: Oh, what the heck, I'll laugh anyway. HA HA HA HA HA HAA! - Batman Beyond: Return of the Joker

More Joker Quotes:

"You can't kill me without becoming like me! I can't kill you without losing the only human being who can keep up with me! Isn't it IRONIC?" - Batman #663

"If the police expect to play against the Joker, they'd better be prepared to be dealt from the bottom of the deck!" - Batman #1

"In my dream, the world had suffered a terrible disaster. A black haze shut out the sun, and the darkness was alive with the moans and screams of wounded people. Suddenly, a small light glowed. A candle flickered into life, symbol of hope for millions. A single tiny candle, shining in the ugly dark. I laughed and blew it out."

"I did it! I finally killed Batman! In front of a bunch of vulnerable, disabled, kids!! Now get me Santa Claus!" - Batman #655

"You really want to know what it feels like to be the clown at midnight? Where there's only ever one joke and it's always on you? Well, here you are. Now do you get it?" - Batman #681

"So... I see you received the free ticket I sent you. I'm glad. I did so want you to be here. You see it doesn't matter if you catch me and send me back to the asylum... Gordon's been driven mad. I've proved my point. I've demonstrated there's no difference between me and everyone else! All it takes is one bad day to reduce the sanest man alive to lunacy. That's how far the world is from where I am. Just one bad day. You had a bad day once, am I right? I know I am. I can tell. You had a bad day and everything changed. Why else would you dress up as a flying rat? You had a bad day, and it drove you as crazy as everybody else... Only you won't admit it! You have to keep pretending that life makes sense, that there's some point to all this struggling! God you make me want to puke. I mean, what is it with you? What made you what you are? Girlfriend killed by the mob, maybe? Brother carved up by some mugger? Something like that, I bet. Something like that... Something like that hapened to me, you know. I... I'm not exactly sure what it was. Sometimes I remember it one way, sometimes another... If I'm going to have a past, I prefer it to be multiple choice! Ha ha ha! But my point is... My point is, I went crazy. When I saw what a black, awful joke the world was, I went crazy as a coot! I admit it! Why can't you? I mean, you're not unintelligent! You must see the reality of the situation. Do you know how many times we've come close to world war three over a flock of geese on a computer screen? Do you know what triggered the last world war? An argument over how many telegraph poles Germany owed it's war dept creditors! Telegraph poles! Ha ha ha ha HA! It's all a joke! Everything anybody ever valued or struggled for... it's all a monstrous, demented gag! So why can't you see the funny side? Why aren't you laughing?" - Batman: The Killing Joke

"Madness is the emergency exit. You can just step outside, and close the door on all those dreadful things that happened. You can lock them away... forever." - Batman: The Killing Joke

"Ladies and Gentlemen! You've read about it in the papers! Now witness, before your very eyes, that most rare and tragic of nature's mistakes! I give you: the average man. Physically unremarkable, it instead possesses a deformed set of values. Notice the hideously bloated sense of humanity's importance. Also note the club-footed social conscience and the withered optimism. It's certainly not for the squeamish, is it? Most repulsive of all, are its frail and useless notions of order and sanity. If too much weight is placed upon them... they snap. How does it live, I hear you ask? How does this poor pathetic specimen survive in today's harsh and irrational environment? I'm afraid the sad answer is, "Not very well". Faced with the inescapable fact that human existence is mad, random, and pointless, one in eight of them crack up and go stark slavering buggo! Who can blame them? In a world as psychotic as this... any other response would be crazy!" - Batman: The Killing Joke

"If I weren't crazy, I'd be insane!" - Batman: Dark Detective

"They could put me in a helicopter and fly me up into the air and line up the bodies head to toe on the ground in delightful geometric patterns like an endless June Taylor dancers routine — and it would never be enough. No, I don’t keep count. But you do. And I love you for it." - Batman: The Dark Knight Returns

"See, there were these two guys in a lunatic asylum...and one night, one night they decide they don't like living in an asylum any more. They decide they're going to escape! So, like, they get up onto the roof and there, just across this narrow gap, they see the rooftops of the town, stretching away in the moonlight...stretching away to freedom. Now, the first guy, he jumps right across with no problem. But his friend, his friend daredn't make the leap. Y'see...y'see, he's afraid of falling. So then, the first guy has an idea...He says 'Hey! I have my flashlight with me! I'll shine it across the gap between the buildings. You can walk along the beam and join me!' B-but the second guy just shakes his head. He suh-says... he says 'What do you think I am? Crazy? You'd turn it off when I was half way across!'" - Batman: The Killing Joke

Quotes from the great George Carlin:

"I think it’s the duty of the comedian to find out where the line is drawn and cross it deliberately."

"It's called the American Dream. Because you have to be asleep to believe it."

"Bullshit is the glue that binds us as a nation."

"If you TRULEY think you have rights I have an assignment for you. Next time you're on the internet, go to Wikipedia, and in the search engine I want you to type in "Japanese Americans 1942", and you'll find out all about you're precious fucking rights"

"When you're born you get a ticket to the freak show. When you're born in America, you get a front row seat."

"Get on the plane!" "Get on the plane!" I say "FUCK YOU I'M GETIING IN THE PLANE!"

"An oxygen mask will drop down in front of you. Place the mask over your face and breathe normally." Well, I have no problem with that. I always breathe normally when I'm in a 600 mile-an-hour uncontrolled vertical dive. I also SHIT normally! RIGHT IN MY PANTS!"