Ubuntu Customization Kit (UCK) is a tool you can use to customize the official Ubuntu Live CDs by adding additional language packs, applications and so on. It doesn't just work for Ubuntu (GNOME), but also for Kubuntu / Xubuntu and Edubuntu.
To make it easy for Ubuntu users to stay up to date with the latest Ubuntu Customization Kit versions, a PPA has been created - for Ubuntu 10.04 Lucid Lynx and Ubuntu 10.10 Maverick Meerkat -, which you can add by using the following command:
sudo add-apt-repository ppa:uck-team/uck-stable
The, install UCK:
sudo apt-get install uck
There is also an unstable PPA (for Lucid only for now) for those who want to try out the testing versions of Ubuntu Customization Kit.
Thanks to Fabrizio Balliano for the news!