XScreenSavers
Here's a list of the modules i've written for use with Jamie Zawinski's XScreenSaver package, a screensaver and locker for use with the X window system.
Gleidescope - an OpenGL kaleidescope.
Invaders - rotating invaders.
SixTenThree - swirling, twisting, fading shapes.
Overlap - er, oscillating, overlapping things.
Tuber - adding another dimension to the classic screensaver.
Blocks - falling blocks.
Making animations from XScreenSaver modules
Here's a little bit of code that'll enable you to make short animations from the output of XScreenSaver modules.