One of the things I love about Deus Ex is all the great dialogue, even the voice acting get's a little hammy at times. Here's a few of my favorite quotes from the game - I encourage everyone to post their favorite lines.

(Hell's Kitchen)
Bum: Stay of the 'Ton, bro. Bad sh** going down!

(Outside Lebedev's Jet)
Gunther: A shame we have to track down and kill one of our most advanced agents. At least we have one of you left.....

(Paris)
JC Denton: Call me nostalgic, but Paris nightlife seems to have lost some of its charm!

JC: "Take your best shot, Flatlander Woman."
Anna Navarre: "How did you know...?"

JC: "Bravery is not a function of firepower."

Weapons Dealer: "Newest model of recoil suppressor, straight from the United Nations Anti-Terrorist Coalition."
JC: "Nice. I believe the UNATCO people would use the term 'harmonic stabilizer.'"
Weapons Dealer: "Yes, they are good at making up nice-sounding words."

Among many:

Walton Simons: "You take another step forward and here I am again, like your own reflection in a hall of mirrors."
JC Denton: "That makes me one ugly son of a bitch."

Bob Page: "Soon, I will become pure energy. I will burn like the brightest star."
JC Denton: "You're gonna burn, all right."

JC: How are the drinks in here?

Patron: Good, if you like rat piss

JC: Never tried it

One of my favorite conversations happened between JC & Isaac (Bartender at the Lucky Money Club):

JC DENTON
The separation of powers acknowledges the petty ambitions of individuals; that's its strength.

ISAAC
A system organized around the weakest qualities of individuals will produce
these same qualities in its leaders.

JC DENTON
Perhaps certain qualities are an inseparable part of human nature.

ISAAC
The mark of the educated man is the suppression of these qualities in favor of
better ones. The same is true of civilization.

JC DENTON
I'll get a drink later.

Here is part of another thought provoking conversation (think of Facebook, Twitter, and other forms of social media):

MORPHEUS
I was a prototype for Echelon IV. My instructions are to amuse visitors with
information about themselves.

JC DENTON
I don't see anything amusing about spying on people.

MORPHEUS
Human beings feel pleasure when they are watched. I have recorded their smiles
as I tell them who they are.

JC DENTON
Some people just don't understand the dangers of indiscriminate surveillance.

MORPHEUS
The need to be observed and understood was once satisfied by God. Now we can
implement the same functionality with data-mining algorithms.

I spilled my drink!

Fixed.

"A forgotten virtue like honesty is worth at least twenty credits." -JCD

"When due process fails us, we really do live in a world of terror." - JCD

"You mechs may have copper wiring to reroute your fear of pain, but I've got nerves of steel." - JCD

Walton Simons: You have nothing. Even if Everett succeeds, you can't synthesize enough vaccine to stop an epidemic. You need a Universal Constructor! And don't think Page Industries is going to leave one lying around for you to use. Not after you blew up the one in Hong Kong.

JC Denton: "I was never properly trained in its operation."

Walton Simons: "Laugh it up, Denton."

http://en.wikiquote.org/wiki/Deus_Ex

Are you sure you pressed the right button?
I do not make mistakes of that kind.
Your hand might have slipped.
No, I wanted orange. It gave me lemon-lime.
The machine would not make a mistake.
It's the maintenance man, he knows I like orange.
So you think the staff have some kind of plot...
Yes, they do it on purpose.

Jump! You can make it!

A bomb is a bad choice for hand-to-hand combat.

"Yevgenni! Yevgenni! Where is Yevgenni?"

STANTON DOWD

"In my opinion, the history of the human race has been one long succession of
conspiracies. To deceive ourselves, we call the successful conspiracies
"governments."

Gunther: 'I am not a machine!'
Denton: 'Sticks and stones.'

I think the best are Morpheus quotes.

"The unplanned organism is a question asked by Nature and answered by Death. You are another kind of question with another kind of answer."

"You will soon have your God, and you will make it with your own hands."