Web ad revenues in the first six months were $11.5 billion, a 15% increase compared with the same period in 2007, according to the Interactive Advertising Bureau (IAB) Revenue Report. The report, which was released on Tuesday, was conducted by IAB and PricewaterhouseCoopers (PwC). It found that search and display-related advertising continue to lead the way for online advertising. Search revenue in the first half was nearly $5.1 billion, compared with $4.1 billion in the same period in 2007; display-related advertising totaled nearly $3.8 billion in the first half, compared with $3.2 billion in the year-earlier period.  Although Web advertising revenues are bucking the generally downward trend compared with other media, the economy is taking a toll on online advertising: Web ad revenue was up 12.8% in the second quarter compared with the same period in 2007, but declined 0.3% from the first quarter.