Linux realtime audio visualizer

Try using projectM.

Either the packages is already in your sources or you can compile the source code from sourceforge.

There are packages for pulseaudio and JACK. ProjectM is able to directly use the audio output or your OS.

cava is a fun one. It's a console application, so it's fairly lightweight. You can also run it in an ssh session from a different computer on the network.

This page [archived] has many different visualizers.

found Synaesthesia to be both beautiful and easy to use, it also works well with pulseaudio through the command

padsp synaesthesia line

website: http://logarithmic.net/pfh/synaesthesia

it is available in ubuntu repositories