Sites I’ve used EE on include:

AdamKhan.net (personal site)

Securosis (import from WordPress)

Always Hungry NY (integration of EE’s search with a create-a-neighborhood feature on Google Maps)

Christian Schools of Florida’s Master Inservice Program (web-based multi-user system)

Take Control Ebooks (import from WebCrossing)

Subtraction (import from MovableType)

For more, see http://www.engaging.net (powered by EE, of course)