Fireworks on the night sky.

D3.js—the top dog when it comes to displaying complex data

Data-drive documents for the web

Either as a base layer for a graph library or for displaying relations in data—if it is about data-driven animated graphics for the browser there is no way around D3.js.

Mike Bostock, its lead developer, creates interactive graphics for the New York Times for a living and has decades of experience in Data Visualization.

Contrary to many other libraries, D3.js does not abstract away the way of rendering (primarily Scalable Vector Graphics, short SVG) from the developer. Thus the learning curve is a bit steeper, but the resulting flexibility and power of this tool is vast.