Uncle Sam Wants You

The famous World War I-era poster of the Anthropomorphic Personification of the United States of America imploring young men to enlist in the military by Giving Someone the Pointer Finger. Usually depicted as an old guy with a beard, a top hat and a suit decorated with the Stars and Stripes. The famous American poster, created by J.M. Flagg (no kidding) in 1917, is actually based on a British poster from several years earlier, featuring Secretary of State for War Lord Kitchener and the famous legend "Your Country Needs YOU".

It is yet another common Picture Pastiche, the most popular Subversion of which is to use the pose as an anti-war protest instead. Other parodies substitute Uncle Sam entirely with some other character wanting you to do whatever they want, whether it is to join some other war effort, to go about with some form of community service, or simply "to shut up."

Compare Sean Connery Is About to Shoot You.

Examples of Uncle Sam Wants You include:

Advertising

In the 80s, ampm convenience stores had an advertising campaign of animated commercials that ended with him pointing and saying, "You want it, we got it!"

Comic Books

In Captain America: Reborn, when Cap is trapped in his own mind after Red Skull stole his body, he sees a variant of this poster with Red Skull saying Red Skull wants you to DIE!
Somewhere out there, there's a cover with The Joker running for president in this format, with the caption Vote for me or I'll kill you!
Obligatory Buffy example: one of the comics has this.
DC Comics has a superhero named "Uncle Sam", the living spirit of America, who has the exact same appearance as the recruitment poster character.

Fan Works

Roboute Guilliman by ArhPriest (on DeviantArt), where said Primarch wants you for Indomitus Crusade.

Film

In Across the Universe, when Max goes in for his Army medical exam, the Beatles song "I Want You" is used, and he hallucinates the poster coming to life, trying to grab him.
From the Reefer Madness: The Movie Musical song "Tell 'Em the Truth": "Let every sir and ma'am / Obey their Uncle Sam / That famous finger's set to point / I want you to drop that joint!"
Right on the cover of Uncle Sam: "I want you... DEAD!"
In Rocky, before the final fight, as part of his all-American act, Apollo Creed is dressed like this and points to the people in the ring and the audience shouting "I want you".
During the USO montage in Captain America: The First Avenger, one of the posters encouraging Americans to buy war bonds features Cap replacing Uncle Sam on the iconic poster. The Uncle Sam poster itself appears during the end credits.
In Daybreakers, posters featuring an Uncle Sam with fangs implores citizens to "Capture Humans."

Live Action TV

Referenced in The Young Ones episode "Boring", where Kitchener from the poster comes to life, sorta, but sits like a waxwork.
Frasier. Frasier is dressed as Uncle Sam in Crock Tales.

Frasier: Dad, I bought you these headphones, so that I wouldn't be subjected to your sports drivel. Please put them on.
Martin: All right, I will. But only if you say it.
(Frasier sighs and points his finger at Martin.)
Frasier: I WANT YOU... to wear those headphones!

One cover of American Dream has titular character replacing Uncle Sam at the poster.
An episode of Arrested Development featured Annyong (Lucille's adopted Korean son) taking on this role for an aggressively patriotic school pageant.

Annyong: I do it. I play Uncle Sam. Better than the part I have now. Guy who order strike on Pearl Harbor.

In one episode of Boy Meets World, Cory and Shawn are riding the subway and they get freaked out when they notice that right behind them is a poster of their principal Mr. Feeny pointing at them with the text "I want you to STAY IN SCHOOL."
The trope is also referenced in Growing Pains when Ben Seavor, shortly after Mike Seavor's arrest for a protest to reinstate the coach of the school, tells the family that various relatives are calling him about the event, and believed they had a relative named "Uncle Sam" until his mom set him straight. It gets even more hilarious when one remembers that after his stint in the series, Mike's actor, Kirk Cameron, would later develop films and documentaries with a pro-American light to them.

Music

Helloween has an album with their pumpkin mascot in this pose. And, of course, the name of the album: I want out.

Periodicals

One Mad Magazine cover had a parody of the poster. Uncle Sam was given Alfred E. Neuman's face, and the caption read "Who Needs You?"
- And in another issue, a back cover with a woman dressed as Uncle Sam pointing at herself, with the caption "I want, too."

Video Games

Fallout 3 has aged posters showing a power-armored soldier helping Uncle Sam to his feet. The caption is something like "Help Out Uncle Sam".
Some sort of version of the iconic "I Want You" poster is seen in the first level of Psychonauts, with Coach Oleander dressed as Uncle Sam.
There's a picture of The Great Khali in this pose in the Smackdown vs Raw 2008 game.
Fable 3's "Albion Needs YOU" posters.
One of Valkyria Chronicles' various promotional posters featured Alicia, the female lead, in Uncle Sam's position.
A Metal Gear promotional poster for recruiting engineers to develop the next game in the franchise has Big Boss in the style of Uncle Sam.

Web Comics

In Sinfest, one of the recurring characters is Uncle Sam, who occasionally gets put in this situation.
The Unspeakable Vault of Doom has "A Word from your God, cultists" version from Cthulhoo.

I WANT YOU
(for my sandwich)

Web Original

Madness Combat has posters in some backgrounds:

The Sheriff wants you. Do not resist. Pull his finger.

The Animutation Gender Neutral features an Uncle Sam poster with the text altered to match a Mondegreen: "I Want You to Be a Total Yutz".
Referenced in the video for the IOSYS song FOE!
Uncle Sam is often parodied on the Internet. His lines are changed to insults like "I want you to find a girlfriend with a name that doesn't end with '.jpg'."

Western Animation

In a Looney Tunes Pepe LePew cartoon, an "Uncle François Wants You" poster appears in a Foreign Legion fort.
The opening sequence for Freakazoid! includes a parody of the poster with the eponymous character as Uncle Sam.
Family Guy. Neil handed Meg a note saying "I Want You". When she looked at him, he was dressed as Uncle Sam.

Other

Political cartoons. Good lawd.

Real Life

The British equivalent, predating the American version by at least three years, is Lord Kitchener Wants You.
- Because, it's fucking on now, chaps.^{[dead link]}
The Russian equivalents, meanwhile, are "Motherland Calls!" (WWII) and "Did YOU volunteer?" (Civil war) (the latter one is the most reminescent of the Uncle Sam poster).
- There's also one Russian Civil war poster of the White army, sayng "Why are you not in the army?". It is also of this style.
Smokey Bear copied the Uncle Sam one with, "Only YOU Can Prevent Forest Fires". Since he's also carrying a shovel, this is occasionally parodied as "Only YOU can help me hide the body".