Rutger Hauer came up with his own final line in the movie himself—that classic "tears in rain" bit. (Source)

At one point, Ridley Scott criticized the film's American crew for being less adept at following orders than British film crews, who would simply respond with "Yes, Guv" to any command. In response, the American crewmembers printed out T-shirts that said "Yes, Guv" on the front of them—with a sassy retort on the back—and wore them on the set. (Source)

The title Blade Runner was taken from a book by Alan Nourse called The Bladerunner. (The term "blade runner" was not actually used in Philip K. Dick's book Do Androids Dream of Electric Sheep?,on which the movie was based.) In Nourse's book, the term refers to something utterly unrelated to anything in the movie—a person who sells illegal surgical instruments. (Source)

Ridley Scott claims that Deckard is supposed to be a replicant, while Hampton Fancher, one of the screenwriters, says that there is no right answer, and it's intentionally ambiguous. On the other hand, Harrison Ford said he intended to portray Deckard as a human. (Source and source)

Ridley Scott and the cinematographer, Jordan Cronenwerth, made the replicants' eyes shine weirdly using a technique called the "Schüfftan Process," which was invented by the great German director, Fritz Lang. It involves bouncing light off a half-mirrored piece of glass at a certain angle. (Source)