The Universe in Chromoscope
The University of Cardiff’s Chromoscope is a fantastic way to visualise different wavelengths—visual, x-ray, radio & more—in the universe. Use the slider to see the differences: you start to see some of the interactions between them.

Not only is this great data visualisation, it’s great astronomy (I’m a bit of an astronomy geek, but only level 1) & a wonderful use of jQuery.