Stefan Sagmeister has to be one of my favourite graphic designers, his work is really expressive and quirky.
Recently I did a presentation on Using Semiotics in Graphic Design for uni, and came across a really interesting and funny podcast of a speech where Sagmeister talks about happiness in design.
Here he makes a great point on a theory on abstraction while talking about an Yves Klein Blue field painting all in the context of design that's made him happy. His observation is that, 'if you abstract an image you merely open as much room for the unrepresentable, and therefore are able to involve the viewer more'.
Less information brings more involvement and engagement.
He also talked about other artists and work that really made him smile & happy and one of them was a New York graphic designer named True.
True with his art work based on signage was the main artist i focused the presentation on, wish I could have seen them displayed it's some great guerrilla art. :)