Mine would have to be from the manga.

Enzo"...Would it kill you this filthy room once and go grab some u.v. once in a while? Or maybe crack open a window? It smells like corn chips and ass in here!"

Unfortunatly, I don't remember much of DMC1 so all my favorite quotes are currently from DMC3:

After Arkham says, "What do you think of the image of your father?", Dante replies, "My father wasn't that ugly. Can't you tell by looking at me?"

Vergil asks for the amulet after defeating Arkham and Dante says, "No way. You've got your own."

"Not very classy for someone's dying words" - Vergil after defeating Arkham

And finally (for now at least), after Dante and Lady have a small fight after Lady discovers her 'dead' father, "I love a fast woman!"

Arkham: "The Legendary Dark Knight Sparda... after awakening to his kind nature, even though he has nothing against his own kind eventually he gained control of them and even defeated the demon god. Detesting himself he fears even more for power. And in the end when he sealed off the demons he also sealed his own powers and sword as well."
Arkham: It's a beautiful legend. This one demon once lived his life as a human with a woman. And finally, as a human, he died in this world. His demonic soul succumbed to his love for a human. He turned into good and the evil spirits sealed off forever.

<Scene changes to an ally, a gang is circling around Vergil while he walks by>
Gang Member1: Ooh, what's this little brother?
Gang Member2: What flashy clothes you're wearing. You really stand out don't you? Ooh look at that sword!
Gang Member3: What a strange one!
Gang Member4: I know what it is! It's a katana!
Gang Member1: Hey Katana Brother, from here onwards the island's ours. Would you mind turning back?
Gang Member1: <While reaching for Vergil's sword> It'd be great if you could just leave this and...
<Has his fingers chopped off>
Gang Member1: Huh!? <He's then sliced in three>
<All the other gang members are then sliced up, Vergil sheaths his sword and continues to move-on.>

Dante: Let me tell you something. Don't you talk about demons in front of me.
Rabby: They are much more honest than humans. "Power is everything", that is the demons unwritten law.
Dante: Thanks for the lecture.
Rabby: If you've had more power your mother may have been saved.

Vergil: ...a key?
Rabby: That's right. The first seal is Temi-Ne-Gru.
Vergil: Temi-Ne-Gru?
Rabby: To activate Temi-Ne-Gru we have to break the seal at four different locations. This is Sparda's seal but with his son it should be easily broken.
Rabby: Next we will release the second seal in the tower. Unlike the first seal this one cannot be broken with mere force. Only those who have the key to the demon world can pass. The key to the demon world is divided into two.
Vergil: Two...
Rabby: Yes. Sparda divided the amulet into two for each of his sons. Two people who were supposed to be one. A key that was once one. Because you were born as two everything was divided into two as well. The same face... the same powers... Sparda's power is evenly divided into two.
Vergil: Are you trying to say that I'm only half as strong?
<Vergil cuts off one of Rabby's ears>
Rabby: No. What I'm trying to say is that both of you are needed to break the seal.
Rabby: <Talking as he falls to pieces from Vergil's attack> Two amulets. Two keys. If both of you do not gather the path to the demon world will not open.

Eva: Pant... pant... pant... RUN... DANTE! You mustn't come out...! Dante! You mustn't! Aaaaa!! No matter what happens keep hiding...
Demon1: Sparda's... human woman. They're dead.
Demon2: All of them?
Demon1: I killed all of them.
Child Dante: Mom... Vergil...

Demon: What is a demon?
Vergil: My father was one. That is where my strength lies.
Demon: Are  you trying to say you are worthy? Would a bird ever know the plight of a lowly mouse?
Demon: Child of a human... You only know of the sky you gaze up at. You are but an existence of limited gratification. Ignorance is bliss. In this world, the instant you realize the vastness of the sky you had only admired in the past... you will die in despair...!
Vergil: The sky is blue. I don't need to travel the world to know that.
Demon: The name you have given us - Greed. Let us rest for now... for the sake of the blue sky we long for.

Dante: It's never a dull moment these days... skeletons throwin' a picnic... long lost brothers dropping in from nowhere, back from the grave.
Vergil: Quite the contrary. I don't remember ever being dead.
Dante: Is that so? Sorry, must've been me not getting the memo.

Vergil: This world shall be consumed by the demonic realm. I will raise a tower. The tower of fear sealed in ancient times. The link Sparda sealed lies there. With my hands, I shall open the link to the demon world.
Dante: Have you lost it?
Vergil: Lost it?
Dante: Reopening the passage our old man sealed?
Vergil: That is the only way.
Dante: The hell? Way to what? A tour? A safari? A haunted house? I ain't laughing!
Dante: Vergil... mother was killed by demons.
Vergil: I know.
*Dante draws his gun at Vergil*

Vergil: Guns and Rebellion. How like you, Dante.
Dante: Yamato? It suits you, Vergil.
Vergil: I am going to the demon world. I will kill all that stand in my way.
Dante: A man like you reduced to a demon's pawn. How sad.