Humour, embarrassment, obscenity, and plain old stupidity. They're all ingredients for a viral video that attracts millions of internet users. Since the emergence of YouTube in 2005, many viral videos have been uploaded to the internet, but few surpass the popularity of the 20 classics we’ve picked out here.

The Coke and Mentos experiments

Who'd have thought that an eighth-grade science experiment would become the object of worldwide fascination? That was the effect of this viral video classic, and people are still checking it out on YouTube and a hundred other viral video sites. You simply drop seven or eight pieces of Mentos candy into a bottle of Diet Coke, stand back, and watch the geysers shoot out.

Hundreds of people have now duplicated the experiment in their own versions of the original video, and the original's creator, Steve Spangler, has done numerous live performances of the beloved trick. Following is what we think is one of the first Diet Coke/Mentos videos to have appeared in shared video land.

Kids lip-synching the Backstreet Boys

One of the first viral hits, the video features two Chinese students (Wei Wei and Huang Yi Xin) passionately lip-synching to the Backstreet Boys' "I Like It That Way" to a cheap webcam. I can't tell whether I hate or love these guys, especially the freaky one on the left (Wei Wei), but I keep watching because I like the guy in the background playing Counter Strike.

According to Wikipedia, the 'Back Dorm Boys', as they've come to be called, were later signed as spokespeople for Motorola cell phones in China.

Bush and Kerry sing 'This Land Is Your Land'

Remember this goody from the 2004 Presidential campaign? One of the first truly viral videos, JibJab's 'This Land Is Your Land', created by brothers Gregg and Evan Spiridellis, recasts the Woody Guthrie classic with places and faces of the 2004 presidential campaign. The original was about pride and national unity, themes that sounded completely out of place in the context of the election, when the cultural gulf between Democrats and Republicans couldn't have been much wider.

But for all that, the big heads of George W. Bush and John Kerry sitting on top of stick-figure, Shockwave-animated bodies was funny in and of itself, never mind the digs that the filmmakers throw at both candidates throughout the video. The 2004 election seems like a decade ago now, but JibJab's video brings it all back, and it's still good for some laughs.

See Bush and Kerry sing

lonelygirl15

Lonelygirl15 is a fake video blog cooked up by Californian screenwriter Ramesh Flinders and his friend Miles Beckett, a physician turned filmmaker.

The star of 'lonelygirl15', a fictional teenage girl named 'Bree', is played by New Zealand actress Jessica Rose. For a long time, people thought the series was a legitimate video blog, until some Los Angeles Times reporters finally outed the creators and the star in September 2006. There's just something about Bree and her so-called life that keeps them coming back for more, even after the series' cover was blown.

The Star Wars kid

This kid had what he thought was a very private moment in the high school production studio. Oh, except that it was taped. A tape rediscovered months later by friends of the Star Wars Kid, who then posted to file-sharing site Kazaa. Within two weeks of its posting, about 2 million people had downloaded the video.

The Star Wars Kid didn't think it was very funny - he sued the families of the 'friends' who posted the video. From the lawsuit: The Star Wars Kid "had to endure, and still endures today, harassment and derision from his high-school mates and the public at large," and, he "will be under psychiatric care for an indefinite amount of time." The Viral Factory, an ad agency specialising in web marketing campaigns, estimated last year that the 'The Star Wars Kid' video had been viewed over 900 million times, making it the most popular viral video ever.

The Numa Numa dance

"The Numa Numa Dance" features a young guy named Gary Brolsma sitting in front of his PC lip-synching, and doing some seated interpretive dance, to a Romanian pop song.

The video debuted at one site back in 2004, and was viewed by more than 2 million people within a couple of months. As viral video sites like YouTube got up and running, millions more saw the video. For many, many people, when they hear the term "viral video," they see the ecstatic face of Gary Brolsma.

Ask a ninja

The concept is simple. This series of web videos, created by Los Angeles comedians Kent Nichols and Douglas Sarine, features Nichols dressed up in a black ninja outfit. He is dead serious as he answers questions sent in by 'viewers'.

"The Ninja is known for his emphatic declarations, as well as his expansive, spontaneous, and often extremely exaggerated hand gestures," says Wikipedia. "Ask a Ninja" episodes are usually about 3 minutes long, and always end with the Ninja signature closer: "I look forward to killing you soon!" (or some variation).

"I'm your manager, Luke" - Chad Vader, day shift manager

In this video series, creators Matt Sloan and Aaron Yonda imagine Darth Vader's kid brother, Chad, as the manager of a grocery store. Hollywood, take note: you can't miss with a premise like that. 'Day Shift Manager' is the most popular of the eight videos Sloan and Yonda have produced so far: It's been viewed more than 5 million times on YouTube, according to the Chad Vader Wikipedia page.

George Lucas in Love

'George Lucas in Love' is a humorous short film made by Hollywood screenwriter Joe Nussbaum, with help from some of his pals from the University of Southern California film school. The film combines and spoofs both Star Wars and Shakespeare in Love.

It has proved to be a huge hit on viral video sites like YouTube. The film portrays a young George Lucas in college struggling against writer's block to write a movie that sounds a lot like Star Wars.

"Leave Britney alone!"

The most recent entry in this greatest hits list of viral videos is also one of the most pathetic: It's the androgynous-looking Chris Crocker's impassioned plea that people "Leave Britney Alone!" Huddled under a sheet, with the camera inches from his face, 20-year-old Crocker pleads, begs, cries, and whines.

It's up to you to decide whether Crocker is serious or is doing some kind of weird performance art. Regardless, Crocker signed a development deal with 44 Blue Productions to make a reality-TV series about his life.

(Warning: The following clip includes profanities)

Leeroy blows the plan in World of Warcraft

This is a way-too-close look into the massively multiplayer online game World of Warcraft and the people who play it. The video features real footage of a botched raid by a team of players, with audio from their teleconference before and during the battle.

To cut a long story short, LeeRoy skips the ultra-serious pre-attack planning meeting (very funny), and attacks prematurely, leading to the deaths of everybody on his team. (Then again, the team's number cruncher estimated that even if they'd followed the plan, they had only a 32.3333, "repeating", chance of survival. Even more disturbing--the captain reports these are better odds than they usually enjoy.) The video was originally posted to some World of Warcraft forums, but because it's both pathetic and hilarious, it spread on viral video until millions had seen it.

(Warning, the clip below includes obscenities)

The grape-stomping lady (with face-plant)

Lights. Camera. Face-plant. Pain and humiliation are staples of the YouTube genre, and this clip is one of the best-known examples. A reporter is out on assignment at a winery somewhere. In a live remote, she is shown on a 5-foot high platform stomping grapes in a small tub. Then she starts doing a little dance with her upper body, and the next thing you know she's falling forward and lands on her face on the ground. Almost as painful is the look on the faces of the anchors when they cut back to the studio.

The Christmas lights house

This viral smash, which began circulating in 2005, features the 2004 performance of a Christmas lights and music show at the house of Carson Williams of Mason, Ohio.

Not only did Williams put up about a billion Christmas lights on his house, but he makes them blink on and off in sophisticated patterns to music by the Trans-Siberian Orchestra. The music was broadcast on FM radio so visitors could listen to it as they drove by the house in their cars.

Tom Cruise on Oprah

The clip of Tom Cruise's blissed-out 2005 performance on the Oprah Winfrey show is creepy enough as it is, but this remix adds a scary animation of what he might really have been thinking.

US comic roasts Bush

Comic Stephen Colbert uses his super-serious faux conservative talk-show host persona on Comedy Central's The Colbert Report to give one of the bravest, edgiest roasts of a president in Washington history at the 2006 White House Correspondents' Dinner.

Colbert lampooned Bush and the Bushites from all sides and all angles, while Bush sat looking clearly uncomfortable and at times stunned. The day after the dinner, footage of the Colbert speech showed up at YouTube and other viral video sites, and has been viewed millions of times since.

Littlest King Kong - the little superstar

Not much is known about the star of this superviral hit. It's a clip from a Tamil Indian movie called Adisaya Pirari from the 1980s. The clip stars an actor who apparently has the moniker 'King Kong'. King Kong is a midget, but one with an odd, childlike look. He's got some crazy dance moves and he smokes a cigarette. Watch at your own risk - it's truly strange.

More cowbell

On April 8, 2000, a Saturday Night Live sketch starring Will Ferrell and Christopher Walken featured 1970s band Blue Oyster Cult in the recording studio cutting their big hit, 'Don't Fear the Reaper'. Walken plays the hotshot record producer who's convinced the success of the track depends on how much cowbell (the cowbell played with abandon by Ferrell) can be put into the mix.

Largely because of this viral video, Generation Y kids could be heard uttering 'more cowbell' to each other and giggling in shopping malls across America in 2004.

See the clip

The worst newscaster in history

It was young Brian Collins' first night on the sports desk. The teleprompter malfunctioned. The teleprompter started rolling too fast. This viral video is a painful (and funny) recording of what happened as a result: one of the biggest broadcast bloopers ever.

The video became so popular that Collins appeared on various TV shows in the US, including the CBS Early Show and the David Letterman Show. ESPN did a story about him too.

Chocolate Rain by Tay Zonday

Tay Zonday is a graduate student from Minneapolis, Minnesota. His YouTube song and video, 'Chocolate Rain', is a little odd, but strangely appealing, and became very popular very quickly in the Summer of 2007. This led to appearances on VH1's Best Week Ever show and the Jimmy Kimmel Live show.

The song's not bad, and the lyrics are cool, but it's the strangeness factor (his head movements, his short body and low voice) that makes this viral video click.

High drama: The dramatic hamster

Millions of people have watched this 5-second video, which consists of a zoom shot of a hamster in a cage as it turns around and looks wide-eyed at the camera.

It's unclear who the original author of the video is, but 'Dramatic Hamster' is one of the most remixed videos on the web. One remixer gave the hamster a James Bond theme, somebody else added a Kill Bill touch - and the possibilities go on from there.