I've seen word clouds popping up in lots of different locations, this one is a Java Applet based versions.
http://wordle.net/
Searching out the best Java applets on the web
Map 24 provide interactive street maps, complete with searching by address, points of interest and full directions, using an applet.
IRIS (Interactive Rich Imaging Software) was one of the most impressive demos at last year's JavaOne conference. It mixes applets with AJAX to provide a photo viewer and editing tool that connects to Flickr to allow you to see slideshows, edit photos and upload photos to your Flickr account.
just2easy provides a full WYSYWYG word processor in an applet, providing the usual text formatting and layout, as well as automatically giving each document you create a unique URL so it can be viewed by anyone with a browser.
This is a really impressive applet based website that allows you to fly around New York, like Google Earth, but also allows you to see details about businesses and buildings, post reviews of places and read others' reviews. I like the ability to click on individual buildings - very cool.