I don't know if it's been mentioned before or not, but this 3D game based on the tv show 'Alias' at:

http://abc.abcnews.go.com/primetime/alias/underground/index.html

is almost entirely written in Java - except for a thin OpenGL/DirectX API JNI wrapper and some native mpeg player code.  It is designed to be multiplayer, but in this case, it's single player only.