Google Blogscoped posts an interesting explanation of the browse sites to target feature on Google AdWords that Inside AdWords announced on Friday. It provides categories of sites with an idea of the number of impressions each site gets per day. Besides  browsing sites by category, you can also target sites by describing the topic, list URLs to check for availability or similar sites.
You can also target a campaign by demographics such as income, gender or ethnicity based on comScore data.  I am curious if there are any head to head comparisons of MSN AdCenter demographic targeting and Google.
About the author
Lee Odden has been recognized as a top B2B Marketing professional by Forbes, The Economist and the Wall Street Journal. For over 20 years he's worked with his team at TopRank Marketing to help elevate the B2B marketing industry through creative marketing programs that deliver more authentic, experiential and inclusive content for brands like LinkedIn, Dell and Adobe. Lee is the author of Optimize and has published over 1.4 million words on his agency's B2B marketing blog. As a trusted marketing thought leader, he has given nearly 300 presentations in 20 different countries on B2B content, search and influencer marketing. When not marketing, Lee is probably running, cooking or traveling.