The Serious Organised Crime Agency is a vital part of the U.K. Government's crime fighting arm. They are the closest thing the country has to the FBI.
They use Joomla for their official website SOCA.gov.uk. The site is an excellent example of a major government organization using Joomla and also of building accessible websites with Joomla: visit their Accessibility page for more details.
Hat tip to Brian Teeman for the find.