This is a collection of organizations that use Debian GNU/Linux

The big list first: http://www.debian.org/users/

City of Munich to use Debian on all 14000+ systems http://news.com.com/Debian+wins+Munich+Linux+deal/2100-7344_3-5689003.html

Vienna, Austria recently decided to move to Debian Linux http://news.com.com/Vienna+to+softly+embrace+Linux/2100-7344_3-5549786.html