Developed at the University of Vigo in Spain, Trisquel is based on Ubuntu. The distro is GNOME-based, but does not use any of Ubuntu's modifications to GNOME. Aside from the branding wallpaper, the largest visual difference is a menu that is arranged by priority, rather than alphabetically, with Internet and Office at the top, and Applications on the bottom.
Designed primarily for Spanish business and finance, Trisquel also includes a Mini, Gamer, and NetInstall editions. Packages for KDE and Xfce are available, but, somewhat confusingly, are labeled kubuntu-desktop and xubuntu-desktop as in Ubuntu.
Trisquel includes Mono-based packages, which although free in license, might deter some of those interested in free distributions from trying it. However, those not bothered by Mono will find Trisquel both fast and almost instantly familiar.
Developed in Argentina, Ututo was the first free distribution recognized by the Free Software Foundation, and remains one of the most active, with versions for Atom processors, as well as for 32- and 64-bit Intel and AMD processors. Although you can also install a generic version of the distribution, if you choose the appropriate build for your CPU, Ututo can be surprisingly fast.
Ututo is the only one of the recognized free distributions to derive from the Gentoo distribution. Like Gentoo, it can use the Portage package tool, but it also includes Ututo-Get, an alternative tool inspired by Debian's apt-get.
Its desktop is a more or less standard GNOME desktop, with a generally standard selection of packages. The last official release was fourteen months ago.
Developed in Venezuela, Venenux does not appear to have any English version, despite the overwhelming number of system messages and packages are in English.
Built on Debian, Venenux uses KDE 3, but apparently as a deliberate choice, not because of the age of the last release. Otherwise, the distribution is currently a year or so from being current, with a standard selection of packages.
These distributions are not for everyone. Some are not for beginners, and you might balk at using the others, since they are typically supported by small groups of developers, and the future of each can be crippled by a very small group deciding to leave the project.
If that is how you look at these distributions, you might consider looking at Debian instead. Debian is not recognized by the Free Software Foundation as an officially free distribution, because it includes the non-free repository, as well contrib, a repository for software that is free in itself, but depends on proprietary software.
However, neither of these repositories is enabled by default, and, in December 2010, Debian announced that its standard build would include a kernel free of proprietary device drivers. These drivers will be placed in the non-free repository, and some Debian images may include them, but the fact remains that in its upcoming release Debian will be easier to install as a distribution every bit as free as the ones mentioned here.
Whether other major distributions will follow Debian's example is uncertain. Ubuntu seems to have rejected the idea several years ago, but Fedora is rumored to be discussing the possibility internally.
Meanwhile, you can consider these eight officially free distributions and Debian the early fulfillment of the free software advocate's long-held dream.