Cue Card

A character holds up a cue card for another character to read, usually while hidden. Expect the reader to be Reading the Stage Directions Out Loud.

Also included are Teleprompters. See also Cue Card Pause, Throwing Out the Script.

Examples of Cue Card include:

Film

Occurs in the end of Shrek.
In The Great Mouse Detective, Mr. Flaversham is forced to read off cue cards while operating the Mouse Queen robot.
In Chicken Little, Turkey Lurkey's aides hold up cue cards to inform him on how to act, including one telling him his fly is open.
In Meet the Robinsons, Bowler Hat Guy is presenting Lewis' invention as his own to the board of a corporation. Doris flies outside the window with cue cards, but then the CEO lowers the blinds, forcing an unprepared Bowler Hat Guy to wing it. Hilarity Ensues.
In Idiocracy, President Camacho starts his speech by declaring "Shit!" followed by a long pause. Cut to the teleprompter which reads "Shit!" and is still slowly scrolling to the next line.
Fatal Instinct: as Ned Ravine is reading a captured bank robber his Miranda rights, his partner holds up cue cards with the words written on them.
Anchorman: The Legend of Ron Burgundy has the main character relying on teleprompters to the point of not knowing what he's actually saying.

Live Action TV

The Sarcasm Sign on The Big Bang Theory.
In the made-for-TV-movie The Adventures of Captain Zoom in Outer Space, Ty Farrel, the actor who plays the hero on a 1950's children's TV show is actually such an incompetent actor that he reads all his lines from cue cards.
Since Saturday Night Live is a live show with guest stars who are often busy or not even actors, they tend to use cue cards. Often for humor purposes, the cue cards are deliberately shown or otherwise used humorously.
- One sketch depicts a morning talk show where the teleprompter suddenly break down. The hosts, without anything telling them what to say for the first time, panic and go completely insane.
When Andy Kaufman guested on Fridays he went (Kayfabe) off script, saying "I can't do this;" cast member Michael Richards went off camera, grabbed the cue cards, and tossed them at Kaufman. Link.
A Spitting Image American special had a send up of Bob Hope who is so dependent on cue cards that he needs a cue card guy to feed the question, "Where are my cue cards?"

Other

Marlon Brando read most of his lines in The Godfather off cue cards. IMDb also says that in Superman his lines were written on baby Kal-El's diaper.

Talk Show

Late Show With David Letterman. "Cue Card Boy" (the guy who holds up Cue Cards for Dave to read) is named Tony "Inky" Mendez.

Video Games

Kingdom Hearts II: This trope is probably the reason for Demyx's popularity. One has to wonder who wrote the cards for him, since half the words don't sound like natural parts of his vocabulary. Observe:

Demyx: "If the subject fails to respond, use aggression to liberate his true disposition." Right. Did they ever pick the wrong guy for this one.

Western Animation

Ed, Edd 'n' Eddy: Edd holds up cue cards for Ed to read while he talks with Johnny. Despite screwing up, he manages to find Johnny's problem.

Ed: Sit down and say hello, Johnny!
Johnny: Uh... hello?
Ed: Ask him how he is!
(Johnny is confused, Edd holds up a sign saying "How are you?")
Ed: I'm fine. A little hungry.

The Simpsons naturally have had their go at this trope. From Krusty pausing during sentences to Homer yelling "NEXT CARD!"