Before deciding between Swing and SWT or Eclipse RCP and Netbeans RCP I'm often asked for some samples for Swing apps.
There are already some impressive applications like: aerith and looking glass (it is almost swing :-)) but they are not "mainstream".
At the Sun's destop site a long list of different Swing applications is available. The application Jake2 is neither Swing, nor mainstream but very interesting :-).
NEW: Online Workhop Effective WebApps without Frameworks is also coming to: MUC Airport.