For me the following between the two demon bosses Dalliah the Doomsayer and Wrath-Scryer Soccothrates in Arcatraz make me stop up and laugh every time.
Wrath-Scryer Soccothrates yells: Did you call on me? Dalliah the Doomsayer yells: Why would I call on you? Wrath-Scryer Soccothrates yells: To do your heavy lifting, most likely. Dalliah the Doomsayer yells: When I need someone to prance around like an overstuffed peacock, I’ll call on you. Wrath-Scryer Soccothrates yells: Then I’ll commit myself to ignoring you. Dalliah the Doomsayer yells: What would you know about commitment, sheet-sah? Wrath-Scryer Soccothrates yells: You’re the one who should be-- Wait, we have company…
The part of Violet Hold that involved the Manastorm couple
Millificent Manastorm says: Finally free from that cursed mage trap! Such a-
Image of Millhouse Manastorm says: Hey there! I was just enjoying a relaxing vacation on the beach when a chilling sense of dread washed over me. Just what are you up to, I wonder?
Millificent Manastorm says: Wait, I recognize that voice...
Image of Millhouse Manastorm yells: Oh buttons, what have you done? Hurry, get her back in the cell!
Image of Millhouse Manastorm says: Now make fun of her hair! It won't help, but it'll make her REAAAALLLLY mad!
Millificent Manastorm yells: Why you... No one insults my hair! NO ONE!
Image of Millhouse Manastorm says: Hoo boy, you really did it!
Millificent Manastorm yells: I know it was you, Millhouse!
Image of Millhouse Manastorm says: Uh oh.
Image of Millhouse Manastorm says: Listen Milly, I can explain!
Millificent Manastorm yells: Don't "Milly" me, Millhouse Jerimus Manastorm! I'm coming for you!
Image of Millhouse Manastorm says: That's not even my middle name!
Image of Millhouse Manastorm says: Thanks a lot. You have no idea what you unleashed upon the world today!
Image of Millhouse Manastorm says: On a completely unrelated note, I... uh... have to go take care of something...
Grand Warlock Nethekurse from Shattered Halls, when fighting the fel orc sacrifices:
You can have that one, I no longer need him! Yes, beat him mercilessly! His skull is as thick as an ogre’s! Don’t waste your time on that one, he’s weak! Ah, what a waste… next!
His pull lines change based on how many of them are standing when you attack the warlock.
For outdoors content, the quest at the start of the Hillsbrad questline where YOU are the questgiver, is pure gold. Its name was “Welcome to the Machine” I think.