Browse the full list of Linux distributions, or jump to the category based on the following list: Commercial, Community, Compact, Desktop, Graphics and Music, Hardcore Geek, Hardware Oriented, Live, Education, Philosophically Free, Security, Miscellaneous.
The Free Software Foundation officially endorses a handful of distributions as being philosophically free -- that is, as containing no proprietary elements such as Acrobat Reader, and being committed to staying that way. These are not the only philosophically free distributions (Fedora 7 could also qualify, and so would Debian without the contrib and non-free repositories), but these distributions are worth considering if you want your computer to match your ideals, or to see how far free software has come and where it still needs improvements.
Ututo: A Gentoo-based distribution, Ututo was one of the first to be endorsed by the Free Software Foundation. It is available in Spanish and English editions, but the English editions are somewhat unpolished.
gNewSense: Built on Debian and Ubuntu, gNewSense is extremely scrupulous about tracking down and eliminating proprietary components -- even down to links to proprietary firmware in the kernel. This focus makes the distribution fine for the desktop, but less than ideal for wireless laptops.
Blag: Relatively new, Blag is a one-CD distro that is based on Fedora, but also includes some programs from less commonly used repositories. Some aspects, like its default desktop, are decidedly eccentric.