Mentioned in Appendix F.I of The Lord of the Rings. Unlike the other war-cries mentioned here, this one takes itself 100% seriously. The films treated the dwarves as comic, and that's an easy enough step, but there wouldn't have been anything comic at all about a swarm of heavily-armoured men with axes, charging at you shouting this. Even if they were short.
2. "The weak shall perish!"
The battle-cry of Species 8472 in Star Trek: Voyager. If you think the sentiment is alarming, just wait until you see one of these guys in the flesh.
3. "Get away from her you bitch!"
Ellen Ripley, in the great Battle of the Single Mothers scene of Aliens. Fight scenes in science fiction can be formal and a bit bloodless, but this one is satisfyingly visceral. Even after watching it many times, you still feel the danger of it.
4. "Resistance is futile!"
The Borg, in the various newer Star Trek series, passim.
5. "Screw you guys: I'm going home!"
Eric Cartman, in South Park, at more-or-less any provocation.
Plus, special awards:
(i) (children's literature division)
Cited for meeting the challenge of representing non-violent violence, and resolve to carry out the same:
Merriman Lyon, in Susan Cooper's Silver on the Tree:
And whoever shall cut the blossom, at the moment when it opens fully from the bud, shall turn events and have the right to command the Old Magic and the Wild Magic, to drive all rival powers out of the world and out of Time.
(ii) (general division)
Cited for defiance in the face of certain defeat, and for general coolness:
Fingolfin, High King of the Noldor,
as described in J.R.R. Tolkien's The Silmarillion:
... He passed over Dor-nu-Fauglith like a wind amid the dust, and all the beheld his onset fled in amaze, thinking that Oromë himself was come: for a great madness of rage was upon him, so that his eyes shone like the eyes of the Valar. Thus he came alone to Angband's gates, and he sounded his horn, and smote once more upon the brazen doors, and challenged Morgoth to come forth to single combat. And Morgoth came.
That was the last time in those wars that he passed the doors of his stronghold, and it is said that he took not the challenge willingly: for though his might was greatest of all things in this world, alone of the Valar he knew fear. But he could not now deny the challenge before the face of his captains; for the rocks rang with the shrill music of Fingolfin's horn, and his voice came keen and clear down into the depths of Angband; and Fingolfin named Morgoth craven, and lord of slaves. Therefore Morgoth came climbing slowly from his subterranean throne, and the rumour of his feet was like thunder underground. And he issued forth clad in black armour; and he stood before the King like a tower, iron-crowned, and his vast shield, sable unblazoned, cast a shadow over him like a stormcloud. But Fingolfin gleamed beneath it as a star ...