Boards
1.2 million copies of "In Rainbows" in ONE DAY.
http://www.gigwise.com/news/37670/exclusive-radiohead-sell-12million-copies-of-in-rainbows
Wow.
First, take into consideration that the album is available for download only. Secondly, consider the album has been hardly advertised outside of various media outlets on the internet.
Radiohead > The music industry