Use the related: query in Google

The data I get from Adplanner and Quantcast is quite different, not to mention limited. Here is a screenshot from Adplanner for autotrader.com

To be honest, I think the results I get from using the related: query is even more relevant than using Adplanner/Quantcast.
Happy PPV'ing and advertising 
There used to be a "Similar sites" link beside the cached link which does the same thing as what you showed, but they seem to have pulled it a month ago.
well damn thats a gem.....still mad at them though for yanking google sets......
Damn It....thats one of my little secrets outta the bag!!
C'mon dudes , the Affexpert "Related Domains" tool uses these and many others for more than a year 
And you can enter up to 100 domains at a time and automate all this.
Another one is the link: command you can use.
-> http://www.google.com/webhp?hl=en#sc...w=1271&bih=889
As keen SEO's always or mostly look for related link properties ;-)