Klima - Go carbon neutral
MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API
Website Carbon Calculator - Find out the how much CO2 your website emits
projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
Padbury Clock Screensaver - Minimal screensaver for Mac
Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.