When the question is about 100% pair programming I'd say there aren't that many. Hashrocket is one of the few companies (I believe Pivotal is, too) where it seems to be true, but most teams that I know are only pairing part of their time.
At Braintree we pair program almost all of the time. There are some small tasks that people will do solo, but 99% of the development on our payment gateway ( http://getbraintree.com ) is done in pairs.
Pivotal definitely does all pair programming
According to the guys I talked to at clojure-conj, most all work at Relevance is pair work. http://thinkrelevance.com/
Thoughtworks does, last I checked
I'd be surprised if that were true, but things may have changed in 8 years.