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About dot com
has a Linux multimedia tutorial. It seems oriented more to playing than to editing.
can be used to edit audio files.
can be used to edit *.avi files.
The podcaster Klaatu recommends Blender
for multi-media editing. (For Klaatu on Blender, see Episode 3x08 at this link
I've used Audacity and Avidemux for very simple editing. I've looked at Blender but never used it.