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.
