Simple gif-display applets. Simplest sound-player applet. Simplest sound-loop applet. Simplest scribble applet. These applets go beyond demonstrating individual basic widgets and into creating new windows and using layout managers to place widgets on them.
Simple frame applets.
Simple menu applets. Java.net Applets Simple UDP applets. Simple TCP applets. Here's an unbearably cute little demo from the Magic Lenses project. I should file this link somewhere else, however grin .