Intense Debate is a sophisticated external comment system for WordPress blogs. From Automattic.
http://www.intensedebate.com
Widgets · Comment System
Get access to data on 21,824 websites that are IntenseDebate Customers. We know of 2,894 live websites using IntenseDebate and an additional 18,930 sites that used IntenseDebate historically and 1,759 websites in the United States.
Get a list of 21,824 websites using IntenseDebate which includes location information, hosting data, contact details, 2,894 currently live websites and an additional 773 domains that redirect to sites in this list. 18,930 sites that used this technology previously and 1,759 websites in the United States currently using IntenseDebate.