http://www.workingwithrails.com/high-profile-organisations
and
Article by Obie Fernandez
Big Name Companies Using Ruby on Rails

List of big name firms that are using Ruby on Rails for major projects:

amazon.com, BBC, CapGemini, BPN, Cisco, C|Net, EA (Electronic Arts), IBM, JP Morgan, NASA, Oakley, Oracle, Siemens, ThoughtWorks, Yahoo!

In addition to the list above, there’s a number of companies where I have direct, or reliably indirect knowledge of Rails adoption through my friends and associates (Obie Fernandez):

John Deere, New York Times, NBC, Barclays, LA Times, Chicago Tribune, Orbitz, Google, Turner Media, Limewire

Notes:

interesting “technology profiler” site : Builtwith.com