AMOR is a nice toy which is absolutely senseless. It displays a tiny figure on your desktop, running on top of your windows or falling down to the bottom. It is a KDE application, but it should be no problem to use it in Gnome (as I do).
In the package are several figures such as the FreeBSD-Daemon, and Tux (in 2 variations). There are also things like a ghost flown from a castle and some more. Some creatures are only static (the FreeBSD-Daemon, Little Billy, and the classic Tux), but the rest are animated. An list of the available themes is provided here.