Even the once-booming online advertising niche has proved vulnerable during the recession.

Interactive Advertising Bureau and PricewaterhouseCoopers issued a new report yesterday, pegging the country's online advertising revenue at $10.9 billion through the first six months of 2009. That hefty number nonetheless represents a 5.3% decline from the first half of 2008.

Despite the dip, there's good news for Google (NASDAQ:GOOG). Paid-search revenue climbed 1.7% during the period to $5.1 billion, now accounting for nearly half of all money that is spent on Web-based marketing. Digital video advertising, a market that Google thoroughly dominates through YouTube, soared 38.3%.

The good news for the industry ends there, though. Display advertising took a small hit, and that's grim news for Yahoo! (NASDAQ:YHOO), Time Warner's (NYSE:TWX) AOL, and smaller players toiling away in graphical brand-based advertising.

The biggest year-over-year plunges took place in online classifieds, email, and referrals. This should be problematic to shareholders of affiliate marketer ValueClick (NASDAQ:VCLK) and online auction juggernaut eBay (NASDAQ:EBAY), as the latter moves to expand its network of free ad-supported classified sites.

The one saving grace in the report is that all of these companies have already posted results for their March and June quarters. The bad news is already out there. As long as these negative trends reverse during the second half of the year, all these companies should bounce back.

Investors who would rather not take chances, and go with the market segments that have proven to be somewhat recession-resistant, have very few choices. They can buy Google, or extend the trend abroad by snapping up international paid-search leaders such as China's Baidu (NASDAQ:BIDU)

Paid search commands a thick 47% slice of the online advertising pie, and it's still growing domestically. You don't want to bet against that.

Are you buying Internet stocks these days? Which ones? Why? Share your tips in the comment box below.

Baidu and Google are Motley Fool Rule Breakers picks. eBay is a Motley Fool Stock Advisor selection Try any of our Foolish newsletter services free for 30 days.

Longtime Fool contributor Rick Munarriz is a huge fan of Google; it would be his homepage, if not for Fool.com. He does not own shares in any of the stocks in this story. Rick is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.