You definitely know two of the three biggest players in mobile display advertising.

Google (Nasdaq: GOOG) is the top dog at the moment with 24% of the market, according to media research giant IDC. Apple (Nasdaq: AAPL) was in second, but recently slipped to third with a 15% slice of the market.

Well, it's time to get to know the name in the middle.

Millennial Media (NYSE: MM) went public today. The country's second-largest player in mobile marketing doesn't have the mobile operating system advantages that Google has with Android and Apple has with iOS, but that's also its strength. Being a stand-alone player in display advertising solutions that are platform-agnostic is paying off. More and more developers are going with Millennial as their one-stop shop for marketing solutions.

And -- let's be frank here -- if you overtake Apple, swapping a bronze medal for silver, you have to be doing something right.

Making a good impression -- all 45 billion of them last month
There are 30,000 apps turning to Millennial for monetization at the moment, including Rovio's wildly popular Angry Birds games. Pandora (NYSE: P) and Zynga (Nasdaq: ZNGA) are also clients. The top music-discovery website and social gaming company saw their revenues rise 99% and 59%, respectively, last year. Millennial is going along for the ride, but the coattails are even better than the savvy developers wearing the coat in the first place.

After seeing revenue nearly triple in 2010, Millennial's top line soared 117% to $103.7 million last year. Yes, that's faster than either Pandora's or Zynga's. It's not just about seeing its clients succeed; Millennial's Rolodex is also growing. The one rub is that the speedster isn't profitable, but losses have been narrowing with every passing year. Based on the 74.9 million shares outstanding after this morning's IPO, its pre-tax deficit last year would have amounted to a mere $0.01 a share.

In other words, Millennial is turning the corner and it's not even stepping on the brake pedal as it does so.

Everybody wants some
Naturally, Millennial's a hot debutant today. The IPO that was originally priced as low as $9 came out last night at $13. It wasn't enough. The stock nearly doubled to open at $25.

We still don't know if display advertising in mobile will be as lucrative as paid search has been for Google. In the dot-com realm, display advertising has been paid search's frumpier kid sister. However, the boom in smartphones and tablets is leading to an explosion in extrapolating eyeballs. Companies want to get their brands out in front of well-heeled users of mobile gadgetry.

A whopping 73% of Ad Age's top 100 advertisers have Millennial accounts. Bonus score: The average that each of these marketers is spending on Millennial has quadrupled over just the past two years.

The world is also open for Millennial. Just 140 million of the 300 million monthly unique users coming across Millennial's graphical ads are in the United States, yet only 10% of its revenue last year came from domestic advertisers. As Millennial's base of sponsors grows as diverse as its reach, revenue and earnings will go through the virtual roof.

The one warning flag here is that Millennial won't be much of a secret after today. At its $13 price, Millennial was valued at nearly $975 million. Today's pop jacks that valuation up to nearly $1.9 billion at the open. Some investors may be naturally skittish of approaching a stock fetching nearly 20 times trailing revenue and a question mark in terms of an earnings-based multiple.

However, we've seen the right growth stocks grow into their lofty valuations. Don't bet against Millennial, either as a fast-growing stand-alone company or as a potential buyout candidate down the road.

Millennial's a hot growth story, but everybody knows it now.

Mobile on the move
The next trillion-dollar revolution will be in mobile, but the best investing play isn't necessarily Millennial Media. If you want to cash in on the upcoming trend, a new report will get you up to speed. Yes, it's as free as this article, but it won't last forever, so check it out now.