Large ecommerce sites that are built on drupal
Drupal Commerce sites: 


http://www.eurocentres.com/en
http://www.commerceguys.com/customers/showcase


Ubercart  sites: 


http://www.topsite.com/best/ubercart


High profile sites:


http://www.infomagnet.com/content/high-profile-high-traffic-drupal-websites


Government sites:


http://govfresh.com/2010/02/5-government-sites-using-drupal-effectively-for-open-government-initiatives/