View Photo Gallery: Internet companies from Groupon and Zynga to Facebook are lining up to go public.

The sheer size of Facebook’s upcoming IPO — now on track for a mid-2012 debut — is staggering, even by gravity-defying Internet standards. The $10 billion IPO would value Facebook at $100 billion, making it the largest Internet IPO ever and the fourth-largest IPO in U.S. history, behind only Visa, GM and AT&T Wireless. In the interest of full disclosure: The Washington Post Co.'s chairman and chief executive, Donald E. Graham, is a member of Facebook's board of directors.

Compare this with Google. When Google went public in 2004, the company was valued at $23 billion, while Netscape was valued at $2.9 billion when it went public back in 1995. Viewed from this perspective, the Facebook IPO deal feels like the defining moment of an era, perhaps the last great IPO of the current Internet boom.

All of this raises an interesting question: Which Internet company, if any, could possibly become “the next Facebook”?

As a rule of thumb, companies are ready to test the IPO waters once they've reached $100 million in annual revenue. By that standard, there are only a handful of privately held Internet companies that would be ready to test the IPO market in 2012, and none of them are even close to the size of Facebook. Now that Pandora, LinkedIn and Groupon have gone public this year, some of the most attractive future IPO candidates include companies like Gilt Groupe, LivingSocial, Yelp and Zynga. Meanwhile, of course, companies like Twitter and Foursquare continue to generate buzz. But these two also continue to struggle with their business models. Will either company ever become profitable - and by the time they do, will we still care?

Most likely, “the next Facebook” has not been created yet. Consider for a moment that when Google was planning to go public in early 2004, Mark Zuckerberg was still a sophomore at Harvard, working on a little project called The Facebook. Concepts such as the “Social Graph” and the “status update” were not yet part of our everyday lexicon? Facebook, like IPO predecessors Google and Netscape, is the type of zeitgeist-defining company that has changed the way all of us think about the Internet.

With that in mind, perhaps the single, best way to predict the Next Big Thing would be to spend a few days hanging out on college campuses in Palo Alto or Cambridge or New Haven, observing how the youth of today are using technology to socialize with one another . The current cohort of college students is, as many have pointed out, the first truly digital generation.

The “next Facebook” will likely have the same world-changing impact on their lives as the graphical browser, the search engine, and the social network did. As the distinction between mobile and the Web continues to blur, it is almost a certainty that the next zeitgeist-defining Internet company will have figured out how to combine our online and offline lives in a way that is seamless, transparent and entirely natural.

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