Visualization Methods

Two guys (Ralph Lengler & Martin J. Eppler) form the Institute of Corporate Communication have developed a "Periodic table" of visualization methods that shows examples of about 100 visualization methods in six categories, which are:

1. Data Visualization - representation of quantitative data in schematic form (either with or without axes).
2. Information Visualization - the use of interactive visual representations of data to amplify knowledge...that is, data is transformed into an image. 
3. Concept Visualization -  methods to elaborate (mostly) quantitative concepts, ideas, plans, and analyses.
4. Strategy Visualization -  the systematic use of complementary visual representations in the analysis, development, formulation, communication, and implementation of strategies in organizations.
5. Metaphor Visualization - displays information graphically to organize and structure information.
6. Compound Visualization - complementary use of different graphic representation formats in one single schema or frame.

Examples: 

SM (Stakeholder Map)

FF (Force Field)

The online version is here:  A Periodic Table of Visualization Methods

This is a great source for thinking of how to illustrate your ideas and data.