] Treemap is a space-constrained visualization of
] hierarchical structures. It is very effective in showing
] attributes of leaf nodes using size and color coding.
] Treemap enables users to compare nodes and sub-trees even
] at varying depth in the tree, and help them spot patterns
] and exceptions.

A very interesting way to visualize a large amount of data on screen at one time.

Smarrtmoney.com has a realtime interactive graph of the stock market using this technology, but its a premium feature.

Treemap: Home page