Concept mapping is a technique for visualizing the relationships between different concepts. A concept map is a diagram showing the relationships between concepts. Concepts are connected with labelled arrows, in a downward-branching hierarchical structure. The relationship between concepts is articulated in linking phrases, e.g., "gives rise to", "results in", "is required by," or "contributes to". (Source: Wikipedia)

PMI on Concept Mapping in Maths Education
Plus: Is quick, allows for brainstorming, and can be collaborative
Why use concept mapping in Maths - http://nrich.maths.org/public/viewer.php?obj_id=5736
Minus: Some suggest it does not have the academic vigor of other activities
Interesting: Traditional pencil and paper or using other freeware e.g. Free Mind

Other links: http://educationalsoftware.wikispaces.com/Mindmaps+and+Charts
Example Sites:
Bubbl.us - http://bubbl.us/
http://trainingvideos.hscs.wmin.ac.uk/mind/index.html

Links
http://arb.nzcer.org.nz/supportmaterials/maths/concept_map_patterns.php
http://www.linkslearning.org/Teachers/1_Math/2_Curriculum_Planning/2_Math_Concept_Maps/index.html