David Ehlers

The JIT is an advanced JavaScript infovis toolkit that was based on 5 papers regarding different information visualization techniques. The JIT implements advanced features of information visualization like Treemaps (with theslice and dice and squarified methods), an adapted visualization of trees based on theSpacetree, a focus+context technique to lay Hyperbolic Trees, and a radial layout of trees with advanced animations (RGraph).

Some very nifty tools here:http://blog.thejit.org/?page_id=14

In particular, check out the spacetree demo 

Also a nice bibliography.

Flare is a collection of ActionScript 3 classes for building a wide variety of interactive visualizations. For example, flare can be used to build basic charts, complex animations, network diagrams, treemaps, and more. Flare is written in the ActionScript 3 programming language and can be used to build visualizations that run on the web in the Adobe Flash Player. Flare applications can be built using the free Adobe Flex SDK or Adobe’s Flex Builder IDE. Flare is based on prefuse, a full-featured visualization toolkit written in Java. 

And view some other visualization api’s here - more links here at reddit

The Google Visualization API lets you access multiple sources of structured data that you can display, choosing from a large selection of visualizations. The Google Visualization API also provides a platform that can be used to create, share and reuse visualizations written by the developer community at large.

Or, if that bores you, simply checkout their Visualization Gallery