Alexa's certified program and pro metrics.
http://www.alexa.com/siteowners/certify
Analytics and Tracking · Audience Measurement · Visitor Count Tracking
Get access to data on 275,797 websites that are Alexa Certified Site Metrics Customers. We know of 18,702 live websites using Alexa Certified Site Metrics and an additional 257,095 sites that used Alexa Certified Site Metrics historically and 6,299 websites in the United States.
Get a list of 275,797 websites using Alexa Certified Site Metrics which includes location information, hosting data, contact details, 18,702 currently live websites and an additional 36,163 domains that redirect to sites in this list. 257,095 sites that used this technology previouslyand 6,299 websites in the United States currently using Alexa Certified Site Metrics.
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Region
These are sites that we think might use Alexa Certified Site Metrics in the future because of their similarity to other sites that already do.