See http://ubuntugamer.wordpress.com/
The goal of this team is to create many game packages for ubuntu that are not yet in the distribution. We only package free games for which the source is available under an open source license. For installing the games packaged by this team, add the repository
deb http://ppa.launchpad.net/ubuntugamer/ubuntu gutsy main
deb-src http://ppa.launchpad.net/ubuntugamer/ubuntu gutsy main
to your sources.list.