Installed Packages

I've been searching for an easy way to itemize all installed packages on a Debian / Ubuntu system, but just found it today. To list all installed packages,

dpkg --get-selections > installed-software

Now, you can use this list to re-install an existing system or duplicate its configuration on a new system:

dpkg --set-selections < installed-software

Finally, run deselect to make the selection changes take effect!

dselect

Thank you to Ubuntu Forums for the answer: http://ubuntuforums.org/showthread.php?t=261366