Dramatic Curtain Toss

Officer: General, in all my years of covering top secret discoveries with sheets, I've never dramatically revealed anything as shocking as this. |DUN-DUN-DUUUNNNN!

—Futurama

There is something hidden under a large, white sheet. You don't know what it is, the characters don't know what it is, but sooner or later, you will. It is inevitable.

Equally inevitable is that when whatever it is behind the curtain is revealed, there will be a great deal of pomp behind removing it. It will be shot in slow motion from four different angles. There will be a collective gasp. This is an important moment. This is the Dramatic Curtain Toss.

A relative to the Dramatic Unmask and subtrope of The Reveal. This can come at any time in a story. Curtain Camouflage is especially prone to it. Any number of reactions may follow.

Examples of Dramatic Curtain Toss include:

Comic Books

There is at least one Archie Comics story where Archie accidentally knocks off the head on a statue of a local businessman; he has it repaired in time for the official unveiling of the statue, but when the curtain comes off, we find out the repairman screwed up and put the head of a pig on instead. Oops.

Film

Shrek the Third: Shrek and Fiona are being introduced at the royal court in confining finery, and Shrek can't reach the itch on his butt. He gets a servant to scratch it for him, and that's when the curtains open...
Played with in Cloudy with a Chance of Meatballs, where the mayor manages to get an entire theme park underneath a tarp, which is unveiled at a televised ceremony.
Megamind has at least two—one during the unveiling of a giant statue (which makes you wonder who makes the giant cloth to cover it up), and one on a picture in Megamind's lair.
Lucy's discovery of the wardrobe between worlds in (the film of) The Lion, the Witch, and the Wardobe, pictured.
- Partially justified, as furniture that is in storage is generally covered with a sheet or tarp of some sort
Done exactly four times in the film of Harry Potter and the Half-Blood Prince, when Draco removes the dustsheet on the Vanishing Cabinet as he attempts to fix it.
The Wizard of Oz: "PAY NO ATTENTION TO The Man Behind the Curtain!"
City Lights opens with the unveiling of a large statue. When the cover is removed, the Little Tramp is sleeping on it.
It's unclear if it happens in the original The Picture of Dorian Gray, but it did happen in The League of Extraordinary Gentlemen...
Occured in Who Framed Roger Rabbit? when Judge Doom pulled aside the curtains concealing his giant Dip spraying machine.
Dramatic Dust Cover Removal: The 69 Charger in the Dukes of Hazzard movie gets one.
The movie adaptation of Ella Enchanted has a statue of Prince Charmant unveiled at a medieval mall.

Music

Dream Theater opened many of their 2009 shows with "A Nightmare to Remember," often starting with a black curtain and pulling it down when the guitar enters. It's quite dramatic.
Japanese band Plastic Tree did something like the above for a filmed live, only dropping the curtain once the song reached its climax. It's really something to see.

Literature

An old high-school English class favourite, Robert Browning's My Last Duchess:

But to myself they turned (since none puts by
The curtain I have drawn for you, but I).

Hamlet does this...but only after he stabs what's behind it (he thinks it's the king; it's actually Polonius).
- Who says I'm fair?
Also used in The Winters Tale, when in the very last act, Pauline reveals the statue of Hermione that she has prepared.

Live Action TV

Happened in an episode of Robin Hood: Vaizey does a dramatic speech while pacing around the room. He finally drops the large curtain in the middle of the room, revealing Robin, dangling from the ceiling.
- Happened again when a large cage intended to hold all the tax money is placed in the middle of the keep.
Happens to Isaac Mendez's paintings in Heroes (multiple times I believe).
Another Dramatic Dust Cover Removal on a car, a Charger in Burn Notice.
Parodied in How I Met Your Mother, when Robin goes on a bender and wakes up in an unfamiliar hotel room. Barney reveals how badly she got out of control by whipping open the curtains, dramatically revealing an entirely un-amazing view of the building next door.

Barney: "That was supposed to be a dramatic view of the Toronto skyli -- you're in Toronto."

Video Games

A Pink Panther game had this, on a pair of gigantic teeth.

Web Comics

Order of the Stick: I guess they really appreciate a good pull.

Western Animation

The Simpsons: Marge's painting of a nude Mr. Burns.
Parodied (what isn't?) on Clone High, where Joan is hidden under a tarp in anticipation for the reveal of her makeover.
Equally parodied in the Futurama episode "Roswell that Ends Well," as the page quote implies.