I've packaged quite a few GStreamer plugins for Fedora Core 3.
GStreamer is kind of a favorite project of mine, I think it is the future of multimedia with Linux on the Desktop because it provides a mechanism by which proprietary media plugins can be installed to add functionallity to a media player without needing to rebuild stuff etc.
The mp3 plugin integrates well with Rhythmbox/totem/sound juicer - and essentially is the same as the livna.org gstreamer mp3 plugin, except they haven't released one for FC3 yet.
The aac plugin works to play aac files in totem or gst-launch-ext-0.8 but does not play aac files in rhythmbox - the problem is aac files are seen as video/quicktime so rhythmbox doesn't want to handle them.
The divx plugin works very well - better than divx in WinXP on same hardware
I have not yet gotten a DVD to succesfully play - I'm still looking into that.
Anyway - the plugins are at http://mpeters.us/linux/fc3_gstreamer.php
These are Fedora Core 3.
Hopefully none of the links are broken ...