Some for the Ubuntu crowd(Note: Using Ubuntu 7.10):
sudo apt-get install p7zip-full
Integrates with Archive Manager, so you can right click a .7z file and select "Extract here"
sudo apt-get install exaile
Very nice music player, similar to amaroK
sudo apt-get install mplayer
mplayer's my prefered movie player, when used with...
sudo apt-get install smplayer
...the smplayer frontend.
sudo apt-get install vlc
Another nice movie player, though not quite as nice(for me) as mplayer
Automatix, while a neat idea, is apparently rather..messy...with its install routines and other things.(Or was, last I heard)
Can also check out http://www.getdeb.net/
for .deb files for various programs that might not be in the repositories. You can select from 32/64 bit 7.04/7.10 packages.