comScore has released the top 50 ad networks and top 50 web properties for June 2008. In ad networks, AOL's Platform-A takes the top spot, reaching 90% of American internet users. Yahoo comes in second, reaching 83% and Google comes in third with 81%. Here's the full list: In web properties, Google leads the pack 140.2 million unique visitors, but Yahoo comes in a very close second at 140.1 million. This past April, Google's sites beat Yahoo's properties for the first time . Microsoft trails in third with 119 million. AOL is in 4th with 110 million and Fox Interactive rounds out the top 5 with 85 million. Here's the chart: ...