For 40k, I actually feel like "An open mind is like a fortress with its gates open and unbarred" is a cooler, if less iconic quote. It just conveys the ridiculous dystopia of the Imperium so well and so quickly.
But yeah gotta love the classic BLOOD FOR THE BLOOD GOD! YOUR CORPSE-EMPEROR WILL NOT SAVE YOU!
I spent a part of my childhood in the extreme north, and you get used to it. Usually I wouldn't see the sun between mid December and late January. Winter just becomes a dark time, and you get used to the street lights. The first sunrise feels almost magical.
Also "We are leaving the universe! How? With enormous difficulty!", but that's more iconic because it rather encapsulates a particular character, rather than being something iconic to a particular piece of world-building.
"I've seen things you people wouldn't believe... Attack ships on fire off the shoulder of Orion... I watched C-beams glitter in the dark near the Tannhäuser Gate. All those moments will be lost in time, like tears in rain... Time to die."
I've never watched Blade Runner, only this scene, but this scene is incredible. And this quote gives a really strong impression of a much larger world.
It isn't very famous, but I like the opening line of Mortal Engines:
It was a dark, blustery afternoon in spring, and the city of London was chasing a small mining town across the dried-out bed of the old North Sea.
It just throws you right into this weird post-apocalypse where cities run around on wheels eating each other. Honestly I think Mortal Engines has some really cool worldbuilding in general.