"Night gathers, and now my watch begins. It shall not end until my death. I shall take no wife, hold no lands, father no children. I shall wear no crowns and win no glory. I shall live and die at my post. I am the sword in the darkness. I am the watcher on the walls. I am the shield that guards the realms of men. I pledge my life and honor to the Night's Watch, for this night and all the nights to come."
And the customary eulogy for a black brother?
"We shall never see his like again. And now his watch is ended."
Star Trek: Any Klingon, any time, anywhere: "Today is a good day to die."
"I am First [name of Jem'Hadar First], and I am dead. As of this moment, we are all dead. We go into battle to reclaim our lives. This we do gladly, for we are Jem'Hadar. Remember: Victory is Life!"
And then Miles O'Brien turns to his men and says:
I am Chief Miles Edward O'Brien. I am very much alive and I intend to stay that way.
While not designed to intimidate as such, the opening narration detailing the mission of the Enterprise (and Starfleet in general) is pretty Bad Ass:
"Space... the Final Frontier. These are the voyages of the Starship Enterprise. Its five year mission: to explore strange new worlds; to seek out new life and new civilizations; to boldly go where no man has gone before."
"We are the Borg. You will be annihilated. Your biological and technological distinctiveness have become irrelevant. Resistance is futile...but welcome."
And then you have this version.... (What?)
"We are the Canadian Borg. Resistance would be impolite. Please wait to be assimilated. Pour l'assimilation en francais, veuillez appuyer sur deux." trans. "For assimilation in French, please press two."
Firefly: Possibly the motto of the Serenity Valley soldiers: "When you can't run, you walk. When you can't walk, you crawl. And when you can't do that, you find someone to carry you."
"I am a leaf on the wind. Watch how I soar."
Battlestar Galactica: "What do we do now, Captain?" Starbuck: "Same thing we always do: fight 'em till we can't."
"What do you hear?" "Nothing but the rain" (The sound of the debris of enemy craft hitting the hull)
Let's not forget Commander Adama's favorite "We've got to roll the hard six."
Colonel Mace: The Sontarans might think of us as primitive, as does every passing species with an axe to grind. They make a mockery of our weapons, our soldiers, our ideals, but no more. From this point on it stops. From this point on, the people of Earth fight back. And we show them, we show the warriors of Sontar what the human race can do.
The overhead announcement on a ship of Sontaran troops: "Battlestations... Rejoice."
In "The Name of the Doctor" we are told that the name Doctor was a promise he had made. We find out in "The Day of the Doctor" what that promise was. "Never cruel, nor cowardly. Never give up, never give in."
The Brunnen-G battle hymn in Lexx probably qualifies:
Yo Way Yo
Home Va Ya Ray
Yo Way Rah
Fighters of the fight
For their home and their heart
We fighters will win or die
Forever we are Brunnen-G
The titular Kamen Rider Stronger proves just how badass he is every time he shows up on screen with his creed.
"The heavens call!
The earth cries out!
The crowds roar!
All calling on me to strike back against evil!
now listen up, villains!
I am the warrior of justice!
The Kamen Rider...Stronger!"
Torchwood provides: "Torchwood: outside the government, beyond the police. Tracking down alien life on Earth and arming the human race against the future. The 21st Century is when everything changes. And you've gotta be ready."
Which, in series 2, becomes: "Torchwood: outside the government, beyond the police. Fighting for the future on behalf of the human race. The 21st Century is when everything changes. And Torchwood is ready."
Parodied on Hey Dude!!. Mr. Ernst tries to psych Jake up for a fight by telling him to remember the Ernst family motto. "We like math?" Mr. Ernst then tells him it's: "An Ernst never backs down!" To which Jake tells him he's never heard of that one before.
"The rich and powerful take what they want. We steal it back for you. Sometimes bad guys make the best good guys. We provide...Leverage."