Services to measure website rankings by traffic have been around for quite some time. The most well known, as it is free, is probably Alexa. The second most well known, however a paid service and much more comprehensive and substantially more data than just site traffic, is Comscore. Others are Nielsen (paid), Compete (free) and Quantcast (free). Still there are more.
Most of the free services, such as Alexa, Compete and Quantcast have site traffic rankings based on unique visitors, page views and other statistics. Each determine statistics of a site differently, some watch which sites people visit and others have you place code on your pages (or both). Other ways to use site traffic services are not just to determine which sites have the most traffic but to determine what type of visitors each site has, whether they have content you are looking for or demographics of site visitors. This type of data used to be obtainable as paid only. In comes Quantcast.
Quantcast Media Planner
Quantcast has free tools to search through sites for you with an easy to use search query. Their results show which sites they obtain traffic data from as a third party observer and which sites have their code installed. If the code is installed there is a much better chance of having accurate data.
Sign up for a free account at Quantcast, login, and choose media planner on the upper menu. The right hand side has your search results and the left hand side has your search options.
The searching capability is amazing. You can see from the graphic on the right that sites can be narrowed down by demographics. Categories such as Gender, Income, Age, and more are available.
These days with privacy concerns so high the amount of data that is actually collected by ad servers to serve up your ad is less than it was years ago. The data you can obtain at Quantcast is about all you can use to target ads. Therefore when determining which sites to advertise on, the Quantcast tool is a great site finder. Use these demographics to narrow your site.
You can also use, in addition to demographics, their category list to find categories to target as well. You may want to target taxes found within the financial services category.
You may then narrow search again based on the minimum or maximum number of US visitors the site reaches each month. Lastly you can export the search results into an excel spreadsheet.
Overall the Quantcast media planner is an amazing tool, especially for free.