A short loop I use in live visuals. Modeled, animated and rendered with Blender.
This one wasn't at all time-consuming in terms of render time, but took a while in human time to get just right. It contains quite a lot of animated objects. The falling block follows different curves (one per impact, for better control), and basically comprises an extended bouncing ball excercise.
Please don't use this without my permission.
Remember to right-click the player and enable looping.