Red Hat Enterprise Linux
The Fedora Project is a Red-Hat-sponsored and community-supported open source project. It is also a proving ground for new technology that may eventually make its way into Red Hat products. It is not a supported product of Red Hat, Inc.
Mandrake, a European Linux distribution with a focus on the desktop.
Debian GNU/Linux.
Developer's site for this simple to use and configure distribution.
One of the oldest Linux distributions, for the nuts-and-bolts folks.
A CD-ROM bootable live Linux distribution. Download it. Boot it. Run it.
Ubuntu Linux is a repackaged distribution of Debian suitable for desktop use.