comScore has released its Media Metrix rankings for the top 50 web properties in the U.S. in August.

And here they are:

Google Sites ranked at the top yet again, with 187 million unique visitors. This is actually down from 190 million in July. Microsoft sites were in second place with 170 million (up from 169 million) and Yahoo Sites were in third with 164 millio (up from 162 million).

Here are the ad ecosystem rankings:

comScore actually revealed a few updates to its methodology this time around.

“The first enhancement is the incorporation of updated demographic universe estimates based on data from the 2010 U.S. census, which provides an improved accounting of the percentage of the population falling into each demographic segment,” the company explains. “The second enhancement was an improvement in comScore’s enumeration survey methodology to better represent persons in cell-phone only households. The third and final enhancement is a new technique to account for cookie rejection in Safari browsers, for sites measured via comScore’s Unified Digital Measurement (UDM) methodology.”

Because of the new methodology, this month’s report excludes the reporting based on month-over-month percentage changes, so we don’t get to see the top gainers this time around.