Scivi is a visualization plugin for XMMS, uses 3D 
Accelerated hardware, but is not actually 3D.

Features:

Low CPU Usage because of 3D accelerated hardware.
All effects including potentially expensive complex 
image transformations are done in hardware. So, if 
you have a fast video card, your CPU most of a time 
will be idle!

Powerful C-style Scripting Language will help you to 
program your own nice presets! The visualization is 
under your control!

Root-window rendering supported. Put a nice video 
effects on your desktop! This feature is window-manager 
dependent. KDE and GNOME probably won't work 
Press 'V' to switch to root-window mode.

Full-screen rendering. Planned.

WWW: http://xmms-scivi.sourceforge.net/