• by Laurie Sullivan  @lauriesullivan, April 21, 2011

The advertising industry likes to think 2011 will be the year of mobile, but with improving economic conditions and a crop of companies bringing in new clients and better-than-expected earnings, they will likely look back to see a solid stream of initial public offerings.

Expect to see an influx of companies go public this year, including those supporting online advertising, according to venture capitalists. Positive economic conditions pave the road for everything from rising stock prices to returning appetites for investors willing to take risks, says one VC.

Conversely, eMarketer principal analyst David Hallerman says the growth and trends promoting digital ad companies to go public point to a crowded market for vendors and other Internet players needing to raise more money to be competitive. And because it's a crowded market, the original investors see now this as a good time to cash out before some companies die.

When Responsys' stock begins trading on the NASDAQ Global Select Market, it will trade under the ticker "MKTG." Earlier this week, the company set the pricing of its IPO at $12 per share of common stock, selling 6,619,654 shares.

Responsys will offer 5,500,000 shares to the public, and 1,119,654 to selling stockholders. The underwriters have been granted an option to purchase up to an additional 967,948 shares of common stock from Responsys and up to an additional 25,000 shares from a selling stockholder to cover over-allotments, if any.

The company, which supports a suite of applications that automates campaigns across channels, has grown revenue at a 42% compounded annual growth rate between 2006 and 2010, from $23.3M to $94.1M.

When Zillow, the Seattle online real estate company founded in 2006, filed for an IPO on Monday, it disclosed revenue performance of $30 million in 2010. The company attributes $17 million to advertising and $13 million to real-estate professional subscribers, according to Lazard Capital Markets.

Zillow plans to raise about $51.8 million in an IPO, which Citigroup is managing. Others on the list ready to go public include online radio service Pandora Media, which filed in February; followed by LinkedIn, which filed in January.

Some report that Groupon plans to pick Goldman Sachs and Morgan Stanley to underwrite its IPO planned for the second half of 2011. The company could be valued for as much as $15 billion to $20 billion.

The positive news some VCs embrace might be found in Criteo's earnings. The company, which supports "paid click" retargeting, saw 70% growth in impressions served, a 90% increase in campaign clicks, and a 13% uptick in average click-through rates for Q1 2011.