Some Web videos get a few thousand views, and more are lost in cyberspace. A few break away from the pack and become superstars, with viewership in the millions. Since YouTube launched in 2005 and made video sharing part of pop culture, viral videos have quickly become the latest mutation in mass media. The viral video is a Web video clip that takes on a life of its own thanks to viewers passing it along through e-mails and instant messages or mentioning it in blogs.

What makes a video go viral? It's not necessarily artistic quality or content. Some are created by Hollywood screenwriters and directors. Some are gleaned from TV news footage and commercials. Many others are amateur creations that strike a chord with Web surfers everywhere.

And it's not star power. In this alternate universe, a hamster running on a piano keyboard has as much of a shot at fame as Britney Spears.

There are sites devoted to measuring the viral-ness of videos. Viral Video Chart serves up the top picks for the day, week, month and year, complete with stats on number of views, blog posts and comments, graphs measuring hits over time, and even a "buzz by language" pie chart. TVWeek.com monitors the top videos from Google, Yahoo, MSN, YouTube, Veoh and others, based on numbers from Nielsen NetRatings.

The power of popular videos has been harnessed by the ad industry. Viral advertising and marketing homes in on target audiences through social networking platforms. In the viral marketing campaign built around the release of "The Dark Knight," a virtual Gotham City was built through Web sites -- TV stations, cab companies and more, which were designed to keep interest high before the film's release.

And millions watch or post TV commercials they like online -- voluntarily. For example, sponsors pay a lot for a Super Bowl spot, but it's an investment with good returns: The ads -- especially the ones that generate buzz -- have a new life on the Web.

The viral video is now an official member of the year-end list of top 10 lists. Here are 10 that made a splash in '08.

1. It's barely 2 weeks old, but the footage of Iraqi broadcast journalist Muntadhar al-Zaidi throwing his shoes at President George Bush during his visit to Baghdad is a late entry in the race. Footage from different newscasts drew more than 2 million viewings on YouTube alone, and also can be seen on Metacafe, Break, Google Video and other sites.

The incident spawned several parody videos, which were less viral, including Funny or Die's ad for an Iraqi discount shoe emporium offering "the most elegant shoes for throwing at world leaders."

2. Election '08 made political videos some of the most-watched online content this year. Barack Obama's road to victory made history on yet another level: It was the first presidential campaign waged in part on video sharing sites. There were the memorable speeches and creative get-out-the vote efforts that went viral. And there were the stars -- Black Eyed Peas frontman Will.I.Am (named the online artist of the year by the Webby Awards) with his "Yes, We Can" video, and "Sexy! Flashy! Wonky! Super Obama Girl!" Amber Ettinger.

3. The separated-at-birth duo of Alaska Gov. Sarah Palin and comedian Tina Fey became two of the year's biggest viral stars. Fey's spot-on imitations of Palin on "Saturday Night Live" became Web classics: More people watched them online than they did on TV.

And Palin's own turkey pardon video, "SNL" and Katie Couric appearances, along with signature wink videos could have been "SNL" skits themselves.

4. When then presidential hopeful Sen. John McCain pegged his opponent as a celebrity, and mentioned Paris Hilton in the campaign ad, Hilton fired back with her own campaign video on Funny or Die, in which she outlined her energy policy and came up with a memorable slogan: "I'm like totally ready to lead."

5. "Christian the Lion" has all the elements of the classic feel-good movie, and it gets it done in less than three minutes. It's the true story of two London men who adopted a lion cub, raised it and released it back into the wild. The reunion scene -- where the grown male lion remembers them and rushes to give them a lion hug, is powerful stuff -- especially those seconds where you're not quite sure just what he's going to do next.

6. Puppy Cam wasn't technically a viral video: It was a 24/7 video stream that quickly went viral, thanks to word of mouth and media coverage. Millions found it oddly soothing to sit and watch a litter of six Shiba Inu puppies eating, sleeping and chewing on their cool toys.

The original stars are moving on to other things, like new homes, but a new litter of Puppy Cam streams is already springing up.

7. Improv Everywhere is a comedy performance art group and prank collective that creates what they describe as "scenes of chaos and joy in public places."

In "Frozen Grand Central," they got more than 200 people to go to Grand Central Station, stop what they were doing and stand motionless for a few minutes. The popular Web video documented the happening, along with confused spectator responses.

Other Improv Everywhere "missions," as they call them, include "Slo-Mo Home Depot," "Food Court Musical" and "Cell Phone Symphony."

8. One of the most watched videos has a local connection that went global. The "Last Lecture" by the late Carnegie Mellon computer science professor Randy Pausch combined wisdom and humor to create a memorable legacy for his students and for everyone else who has seen it. As Web video goes, it's long, weighing in at more than an hour, but Pausch's message of understanding how to enjoy life, even in the face of death, resonated with millions.

9. When video game designer Matt Harding quit his job in order to travel in Asia five years ago, he made a goofy little video of himself dancing during one stop and posted it online for friends and family. Stride Gum ended up underwriting two more trips. Now there's footage of Matt and a global group of dancers doing the same little dance in beautiful places all over the planet.

10. "Prop 8 -- The Musical" took on the anti-gay marriage lobby with a fast-paced musical revue starring Jack Black as Jesus. Created by composer Marc Shaiman, the cast also featured John C. Reilly, Neil Patrick Harris, Margaret Cho, Andy Richter and others.

The video arrived online after Californians voted on the measure to ban same-sex marriage, but as one of several videos on the subject that have gone viral, it touched a nerve and fueled another round of discussion on the subject.