SEO based plugins from Yoast.
http://yoast.com/wordpress/seo/
Widgets · WordPress Plugins
Get access to data on 14,604,418 websites that are Yoast Plugins Customers. We know of 2,000,001 live websites using Yoast Plugins and an additional 12,604,417 sites that used Yoast Plugins historically and 1,039,634 websites in the United States.
Get a list of 14,604,418 websites using Yoast Plugins which includes location information, hosting data, contact details, 2,000,001 currently live websites and an additional 1,729,868 domains that redirect to sites in this list. 12,604,417 sites that used this technology previously and 1,039,634 websites in the United States currently using Yoast Plugins.