What's the key to a successful cinematic infodump?

Infodumps are a double-edged sword. They allow filmmakers to cram a ton of worldbuilding into a short amount of exposition but can also bludgeon the audience into a glassy-eyed stupor. What's the secret to cramming plot into the audience's earholes?

Over at The Wrap, Michael Lee analyzes what makes the infodumps of three recent blockbusters effective. For example, Avatar had spectacular visuals to bolster potentially clunky exposition, and Inception used the naivety of Ariadne and Saito to explain the vagaries of extraction. Lee identifies the documentary format of District 9 as a particularly ingenious means to both inform and entertain. Lee rightly notes:

"District 9" opens with a fake news segment on the alien Prawns. It could almost be the opening for a real "Frontline" report. The documentary technique gets us right into the backstory of the world with its alien refugees in South Africa. We see random people talk about the Prawns, we see the signs for Aliens to stay out. Immediately it taps into our collective conscience about apartheid and segregation as well as conveying the main premise of a shanty town made of alien refugees. It's so clean and efficient that at first glance we don't realize that Shartlo Copley's Wikus is our protagonist. A lesser film would have just used this as a teaser section and killed Copley off. Writer/director Neil Blomkamp was smarter than that and the result was one of last year's breakout films and performances.

How about you, dear commenters? What science fiction infodumps did you find seamless, and which made your tympanic membrane collapse under their sheer leadenness? I'll go first — I've always been partial to the "IV drip infodump" of Escape from New York. The movie gives audiences a vague future history of NYC (and an equally nondescript map) at the beginning...

After telling you exactly what it's about, the movie uses minutiae and unexplained lines (particularly those about Snake's history — everyone thinks he's dead!) to flesh out this spartan synopsis. The world aggregates in drips and draps. Heck, these disposable lines gave William Gibson plot fodder for Neuromancer. Said Gibson:

[The movie] had a real influence on Neuromancer. I was intrigued by the exchange in one of the opening scenes where the Warden says to Snake: "You flew the wing-five over Leningrad, didn't you?" It turns out to be just a throwaway line, but for a moment it worked like the best SF, where a casual reference can imply a lot.

So, what infodumps are your faves?