That online display advertising growth so many digital marketers have been anticipating may be arriving a little early. According to a new report from Rubicon Project, digital ad spending grew 47% during the first half of the year.

That’s not including search revenues — and despite an economy that has yet to nudge past the brink of rebound.

The economy has rebounded slower than predicted this year. Economic growth started off well in 2010, with the economy expanded at a rate of 3.7%, but in the second quarter that growth slowed to just 2.4%.

Meanwhile, display advertising is growing at a fast clip. Marketers have expanded their budgets and 2010 is expected to be the strongest year for online ad spending.

In 2009, internet ad revenues (minus search) slowed, but totaled $5.9 billion in the first quarter of 2010, according to the Interactive Advertising Bureau (IAB) and PricewaterhouseCoopers (PwC), the highest number since the companies started tracking internet revenues.

According to the Rubicon 20 Index, which tracks 20 premium publishers that include NBC
Universal, Time Inc. and Gannett, CPMs rose an average of 25% from the first quarter of 2010 to the
second. Overall,
the Rubicon 20 Index grew 47% from the
start of 2010
through the end of the second quarter.

U.S. Web users now
receive 15% more display ads since 2009, according to
comScore’s Ad Metrix. comScore also estimates that the total U.S. display ad
spending for the first quarter of the year reached $2.7 billion.

Meanwhile, Borrell Associates estimates online ad
spending is poised to grow nearly 14%, from $45.6 billion in 2010 to
$51.9 billion in 2011. Much of that growth is coming from local ads. The company predicts by next year, local online advertising should
grow by almost 18% — from $13.7 billion in 2010 to $16.1 billion in
2011.

According to Borrell, targeted display advertising will grow nearly 60%
in 2011, reaching $10.9 billion. While national advertisers are expected
to ramp up their use of targeted display by about 50%
, local
advertising will more than double to over $2.3 billion in 2011.

These numbers are good news for those bullish on display advertising. As growth in the search advertising market begins to slow, that’s getting to be more and more companies. For one thing, display advertising is quickly changing to include more formats and advertising approaches.

Just yesterday, Jonathan Bellack, Google’s director of product management, explained in a post titled “Everything is going to be ‘display‘”:

“Looking forward, what we call “display” today will just be
“advertising”—a single platform that can coordinate an advertiser’s
campaign across streaming audio ads in car stereos, interactive mobile
experiences on smartphones, and HD video ads on set-top boxes. Imagine
if that single platform could optimize the campaign, automatically
delivering the best-performing ads, best returns and best mix, across
all those platforms. That’s the future we envisage.”