Drupal Sites
Here is a list of Government and other large sites using Drupal, with links and screenshots for each site. These are great examples of the flexibility and power of Drupal as a Content Management System (CMS).
http://www.whitehouse.gov/
http://www.commerce.gov/
http://www.energy.gov/
http://www.bestbuymobile.com/
http://www.ed.gov/
http://www.theworld.org/
http://www.nasa.gov
http://www.popsci.com/
http://www.economist.com/
http://www.mtv.co.uk/
http://abcdigmusic.net.au/
http://www.digitaldollhouse.com/
Here are 1300 more Drupal sites, many with links to case studies