www.aharef.info/2006/05/websites_as_graphs.htm

This processing based applet visualizes the HTML DOM structure of any website, with different coloured nodes representing different HTML tags.

http://www.aharef.info/2006/05/websites_as_graphs.htm

You can see loads of the generated visualizations at Flickr.

benfry.com/traces/

The Preservation of Favoured Traces is a Processing based applet that visually displays the differences between various revisions of Darwin's Origin of Species.

benfry.com/traces/

turbulence.org/spotlight/thinking

The Thinking Machine is a Processing based applet that will give you a good game of chess, but the cool thing is that while it is thinking about its next move it shows you the potential moves that it is considering, using coloured lines.

http://www.turbulence.org/spotlight/thinking/

http://www.processing.org/

Thanks to Rex Guo for the tip.