This is a poster from the American Statistical Association that I took from http://www.mathaware.org/mam/08/theme.poster.html
What make this poster successful is how minimalist and direct it is. It shows the point directly and at the same time is creative in the way the head and the interrogation mark are connected. Also, there is a perfect harmony between graphics, typography, and color. Moreover the diagonal make by the direction of the head and the type gives the design a dynamic feeling and connect us to the important imformation.