At the last JavaONE 2007 conference an impressive application called IRIS was presented. It is a nice looking web app combined with an ...applet. It is a photo manager application with a slick 3D viewer, explorer and even editor. Iris even supports Drag'n Drop between the desktop and the browser. The fusion between Java and AJAX makes absolutely sense from the development and maintainability perspective.
You can try it out here (Use e.g. the name "romainguy" to find some photos) or watch the demo on youtube. The source code is available as well. However this app is already outdated - it wasn't built with Java FX Script and especially Consumer JRE (both technologies were announced on the same JavaONE :-)). The startup of the applet would be faster then, Java FX Script could provide even more impressive look and feel and simplify the implementation.
Java FX demos are impressive as well - the easiest way to try it out - install the netbeans 6.0 plugin and start e.g. the Weather Application.