I am addicted to gigapedia (now library.nu) and I download several archives everyday which are password protected.
I wrote this very simple script to extract all the archives (7z, rar or zip) in a given directory by testing a list of preset passwords.
It uses 7z, unrar and unzip.

If you want to try it,

1) Edit 7z_extract.sh and add the passwords you want.

2) Copy 7z_extract.desktop to
$HOME/.kde4/share/kde4/services/ServiceMenus/
OR
$HOME/.kde/share/kde4/services/ServiceMenus/

3) Copy (as root) 7z_extract.sh to somewhere in your path (/usr/bin or /usr/local/bin) and make it executable, i.e.:
sudo cp 7z_extract.sh /usr/local/bin; chmod a+x /usr/local/bin/7z_extract.sh


Its usefulness is very limited, since it comes in handy only when you frequently extract files with a fixed series of passwords.