Art of Illusion: Art of Illusion is a 3D-modeller, renderer and raytracer. It is written in Java and runs on Linux, Solaris, OS X, Windows and probably more.
Cinelerra: Cinelerra is a full-featured non-linear video editor for Linux.
Cthugha Development Page: "An Oscilloscope On Acid" - Cthugha also lets you save certain visualizations to keystrokes which makes it a great tool for VJs.
GStreamer: GStreamer is a multimedia framework for Linux with that can use plugins.
Ice Sound Manager for IceWM: Ice Sound Manager is a Gtk-based sound events and sound theme manager for IceWM that does not require Gnome.
LINGOT is Not a Guitar-Only Tuner: GPL musical instrument tuner, originally conceived to tune electric guitars.
Matan Ziv-Av: zgv, svgalib, and other Linux projects.
MPlayerXP: MplayerXP is branch of the well-known mplayer which is based on a new, thread-based core. The new core provides better CPU utilization and improves performance of video decoding.
O'Reilly Network: Streaming Media With Linux Resources Page [Mar. 30, 2001]: An Internet guide to the tools and software you'll need to receive and broadcast streaming media with Linux.
OpenQuicktime: An opensource multimedia library to play, edit and author Apple Quicktime movie files.
PRTSoft - Home of MP3 Splitter: MP3 Splitter takes your large MP3s and breaks them into equal sizes that you specify.
The Linux MP3-HOWTO: The Linux MP3-HOWTO.