The sole author of Impropmptu, Andrew Sorensen, is also currently the best live performer. Some chosen samples:

A study in Keith: a poignant piano part http://vimeo.com/2433947. When the code is evaluated (usually one function at a time), you can see the code block flash in a pale yellow/green color.

Stained: This one comes with visualizations. Simple yet psychedelic. http://vimeo.com/2502546.