https://github.com/280north/cappuccino/wiki/Current-Projects
A fairly recent impressive Cappuccino application is PicsEngine:
http://www.picsengine.com/
Also check out GitHub Issues which very nicely demonstrates the state of the art TableView widget:
http://githubissues.heroku.com/
Archipel is more of a technical app highlighting a ton of various '2.0' techs in one app unified by the Cappuccino experience:
http://archipelproject.org/