The Yollege.com social network for college kids http://yollege.com (How I spent my fall and winter 2008, wrestling drupal/panels2 into submission...)
Moodle sites for teachers in K12 http://moodle.eastbayschools.net
A google earth based collaborative authoring environment, including video synchronization: http://gearth.eastbayschools.net
A redesign of Canyon Middle School's web site, using Drupal as a CSM framework in a K12 environment: http://canyoncondors.eastbayschools.net
A content management system used by the Exploration Life Support group at Nasa Ames Research Center (uses a precursor to the open source qcodo framework, available at http://qcodo.com): http://opis.arc.nasa.gov
AthenaRMS, an issue tracking system primarily used for businesses for customer support, but also finding other niche markets, including being used to track student progress through a specialized program, including English as a Second Language (ESL) . http://athenarms.com