JavaScript Graph Visualization Tools
A collection of JavaScript graph visualization tools that look promising to me.
D3.JS
Link: http://d3js.org/
Sigma.js
Link: http://sigmajs.org
And a plug-in for custom node shapes and images: https://github.com/jacomyal/sigma.js/pull/106
Canviz
Link: http://www.ryandesign.com/canviz/ (builds on Graphviz)
VivaGraphJS
Link: https://github.com/anvaka/VivaGraphJS
It has some really fast examples, good performance.
JavaScript InvoVis Toolkit (JIT)
Link: http://philogb.github.io/jit/demos.html