A Lighter Ubuntu

To display all of the installed packages in Ubuntu (installed via apt) by size, use the following command:

dpkg-query -W --showformat='${Installed-Size} ${Package}\n' | sort -nr | less

To uninstall packages completely as if you were making a live-cd, use:

apt-get remove --purge package name

There is a new package called remastersys in the repositories that make creating a live-cd simple.
The howto can be found at:
http://www.howtoforge.com/ubuntu-linux-mint-livecd-with-remastersys