Water colour pencil on paper
Everyone draws. Even if it means just doodling in the margins of boring textbooks or scrawling all over the page during insufferable meetings or scribbling in the pad during (or after) a contentious argument. At some point in time one takes the drawings away from the margins and puts them in the center of the page. But the purpose for drawing remains the same. An attempt to put one's thoughts in order. A silent argument between the hand that wields the pencil and the mind that wields the hand. A stream of conscious effort whereby one lets the subconscious wade through stormy tides. Whatever the story behind the humble sketch one thing, as anyone who has ever doodled knows, is certain– doodling helps one think clearly. Often when one puts the pencil down one feels, for want of a better word, refreshed.
I never have doubted the fact that people who doodle during lectures or meetings are able to process the information being given, if not 'better', then at least 'differently' from the others who merely listen. Here's a TED talk that makes the case for unlocking your brain via pad and pen: Sunni Brown: Doodlers, unite!