I would think the dot . is the most versatile. It can signify the end of a sentence. Three in a row ... signifies that a list goes on and on. One on top of each other : et voila, your list starts. On top a comma ; signifies a change of direction in a sentence.

In front of a bracket and you have eyes : )

AND place them strategically and you have braille.*

(* or chicken pox)