Vanilla: Sylvanas Windrunner: “We are the Forsaken. We will slaughter anyone who stands in our way.”
BC: Illidan: "Akama. Your duplicity is hardly surprising. I should have slaughtered you and your malformed brethren long ago.”
WotLK: Algalon the Observer: “I have seen worlds bathed in the makers flames; their denizens fading without even a whimper. Entire planetary systems born and raised in the time it takes your mortal hearts to beat once. Yet all throughout, my own heart, devoid of emotion, of empathy, I. have. felt. NOTHING. A million, MILLION lives wasted! Had they all held within them your tenacity? Had they all loved life as you do?”
Cataclysm: Deathwing: I AM DEATHWING. The destroyer. The end of all things. Inevitable. Indomitable. I AM THE CATACLYSM."
MoP: “ Garrosh Hellscream: Anger, hatred, fear, they are weapons of war. The tools of a Warchief. Yes, yes, I can see it now. I can see the future of this world. A world ruled by the Horde, my Horde! The old one calls to you. The heart will be your end. See the visions of fear, despair and doubt as I have. You will be trapped for eternity . The true horde will come to pass, I have seen it! I have seen mountains of skulls and rivers of blood, and I will have my world!"
WoD: Draka: You fight with much experience, Thrall. Why do you not have a mate?
Thrall: I-I do! I saw that my mate remained behind to care for our little ones.
Draka: You… wanted her to stay? This is war! More than ever, this is when family belongs at your side!
Thrall: I… never looked at it that way.
Draka: What a strange green orc you are.
Legion: Runas the Hungere: “This hunger is consuming my very mind. It is taking every ounce of my energy to just… just… Can you hear me, my friend? I… I can not see you anymore. I think… perhaps it is time to say goodbye, then. Thank you, my friend, for letting my last few hours mean something.” 
BfA: Meerah: “Dolly and Dot are my best friends…”
Honourable Mention: Yogg-Saron: Uulwi ifis halahs gag erh’ongg w’ssh.