Quadrant Chart is a good instrument for showing the data that has two or three measurements, which can be represented by two axes and the Bubble (marker) size. Also they are used for planning quite often. For example, Quadrant Chart can be used for building a BI services comparisont.
This Chart is a Quadrant with countries shown as markers with two measurements: quality of life and pollution index. There are two annotations, revealing the worst and the best countries for living - the higher the quality of life is and the lower the level of pollution is, the better life is in the country.