A quick rundown of major Linux distributions (distros)
This is a brief run down of the various distributions, some strengths, and target audience.
Debian – Debian is one of the longest running distributions. Debian stable (currently 3.1) is terrifically stable and powerful. Debian uses APT (advanced packaging tool) which makes installs and dependency handling very easy. By the time Debian stable comes out it is usually much more dated than FC for example, but updates to applications are constantly being made. Debian is similar to FC, having a working knowledge of Linux is very helpful for installing and maintaining Debian. Debian is all about choice, it has the most packages available, and covers the greatest amount of platforms (from SPARC64 to ARM, to X86). Debian is one of the mainstays of Linux, and many other distributions are based upon it. See http://en.wikipedia.org/wiki/Debian for more details.
Gentoo – Gentoo is another venerable distribution. Although installers are available Gentoo is usually compiled from souce code. This makes Gentoo very fast, and optimized for the computer on which you run it, but it makes installation difficult, slow and painful. Gentoo is very powerful, USE flags are terrifically useful, and offers bleeding edge packages. Gentoo is not meant for a first-time Linux user, but for a user who is comfortable with Linux and wants more power. See http://en.wikipedia.org/wiki/Gentoo for more details.
Slackware – Slackware has been around for a long time as well. Slackware is simple, from a design perspective rather than end-user. Rather than pushing for customizability, Slackware has emphasized a UNIX-like management. There are few GUI tools for Slackware, and only KDE is supported officially. SuSE was originally based on Slackware. Slackware is free to get and use. Slackware is not for a novice user. See http://en.wikipedia.org/wiki/Slackware for more details.
Fedora Core – Fedora Core is a branch off of RedHat. RedHat was nearly the only viable Linux distribution for years. It continues to lead Linux in corporate environments, especially as servers. Fedora Core is a fork of RedHat. RedHat costs money, it is targeted at corporations, while Fedora Core is not and is free. Images can be found quite easily. FC is comparable to Debian. You should have at least working knowledge of Linux (or read a lot of man pages) to get FC to work properly. FC is typically an even balance between stability and cutting edge. The current release is FC4. See http://en.wikipedia.org/wiki/Fedora_Core for more details.
SuSE – SuSE (prounounced susee, or alternatively suze) is Novell’s answer to the RedHat corporation. SuSE is quite easy to use, since Novell has tried to fashion it as a desktop and server distro. SuSE won’t be as up-to-date as FC, but it is very easy to install and use, it has good hardware detection, and runs very smoothly. Yast (the SuSE installer) is probably the easiest installer around. Novell distributes (online) liveCD’s free, but if you want the most recent official professional version, you’ll have to buy it. Old and unofficial versions are available free of charge. See http://en.wikipedia.org/wiki/SuSE for more details.
Ubuntu – Ubuntu is the new kid on the block. A Debian based distro, Ubuntu supports only Gnome, though Kubuntu supports KDE. Ubuntu is designed for ease of use, and simplicity. Ubuntu is an easy distribution to start on, and offers predictable support and releases. See http://en.wikipedia.org/wiki/Ubuntu_Linux for more details.
Mandriva – Mandriva is easy to use. Formerly Mandrake & Connectiva (two different distributions merged into one), Mandriva focuses on end user simplicity. Images are free, but support is not. I have used Mandriva, and I must say, it is one of my favorites. The three CD’s it comes in, contain buckets of prepackaged RPMs, most of which you’ll never use. Installing is as easy as any distribution, and hardware detection is quite thorough and automatic. Current version is 10.2. See http://en.wikipedia.org/wiki/Mandriva for more details.
Knoppix - Knoppix is a Debian based distribution. Released as a Live-CD, Knoppix can be installed permanently on a system. Knoppix has excellent automatic hardware detection, and is free to get and use. Knoppix seems to be used most often to save Windows (or other OS) boxes, when things go on the fritz. It is also an easy introduction to Linux. See http://en.wikipedia.org/wiki/Knoppix for more details.
Xandros/Linspire (Lindows) – Xandros and Lindows are very similar. Both targeted at end users, both must be purchased. Both are based on Debian, have been criticized for security issues, and are very easy to use. LiveCD’s are available, for free, for both distributions. See http://en.wikipedia.org/wiki/Xandros or http://en.wikipedia.org/wiki/Linspire for more details.