"HowTo: Create a list of installed packages
I found out how to do this recently and thought it might be helpful to some people. To output this information to a file in your home directory you would use,
dpkg --get-selections > installed-software
And if you wanted to use the list to reinstall this software on a fresh ubuntu setup,
dpkg --set-selections < installed-software
Smart! -- So I put the resulting installed_software file on my ftp space.