From Compsci.ca Wiki
Ubuntu is a Debian based distribution of linux. It is quite popular among CompSci.ca users, and has a great community. It is free of charge, as well they will ship a CD of the current version for free.
Their release schedule, is based on the release of the GNOME desktop environment, where they (Ubuntu) release one month after.
Long Time Support Version
Ubuntu also has a LTS (Long Term Support) version, which they release every two years, and provide support for the desktop for 3 years, and 5 years for servers.
The current LTS version is, Hardy Heron (8.04 LTS) released on April 24, 2008. It will be supported on desktops till April 2011, and for servers April 2013.
The next LTS version is set to be Lucid Lynx (10.04 LTS), which is planned for release on April 2010, and would be support on the desktop till April 2013, and April 2015 for servers.