The more funny and easy and gratifiant is Chaoscope ;) (free)
http://www.chaoscope.org/
File/New (choose curves family)
F3 Start (Press any time you want for a new random parameters)
F4 Calculate
Esc Stop
I don't resist to make another one at each time I name it :D



here of the day! :) Take 10 seconds for all! (research - render)