A decent computer and lots of volume is recommended.
Well, due to the fear of slipping behind, I felt I better start learning the new Flash language, Actionscript 3, and at first glance, one of the coolest features is definitely the SoundMixer.computeSpectrum function. Read : AS3 Music Visualisation »
Smack My Glitch Up AS3 BitmapData Glitch Generator
More Music Visualisations A Second Helping of Retinal Nourishment
3D Ribbons in Papervision Ribbon3D Class for Drawing 3D Lines and Ribbons in Papervision3D
Bandcamp Music Visualisations Avant-Gard Audio Ocularisms with AS3 ComputeSpectrum
2D Cellular Automata Actionscript 3 Game of Life
Distracting but cool addition to pub pool: http://bit.ly/ePloh