Advertising Age

The Advertising Age website includes a list of the 150 most popular websites in the world.

They use metrics from 3rd party companies to position you in the top blogs. Note that you will get a link from there website once you make it to the top... You are free to submit your site, although you need to reach a minimal level of popularity to be accepted. They express that popularity using 150 points computed from different sources such as Alexa and Yahoo!

Being at the top of that list is an excellent proof that your blog is worth a lot of money for advertisers... (not AdSense!)