Stamps of balled-up paper!
I got bored and experimented. This is 4 different paper ball brushes (and a blender), made of scanned crumpled up paper. 



The more complex ones look best at large sizes:

There is also a simpler one you can use to paint/texture, and a blending brush. Feel free to adjust the gap & blend to get it right for your art. :)

have a ball