Adwords Site Selection is an incredible resource. This allows you to choose which sites on the Google advertising network on which you place your ad. These advertisements do not appear on the search pages, so need to be specifically created for the sites on which they would appear. Competitor tagging is the obvious use of this tool. Done right, it can more than double relevant response rates from the content network!
Google now offers demographic selection as a part of its site selection based adwords campaigns. You can choose from sites sorted by their demographic classifications. I’m testing it now with clients and will probably blog about the results. It doesn’t look nearly as good as MSN Adcenter’s setup, but just wait.