Classic Flavors

Debian

 * Difficulty: Beginner/Intermediate
 * Desktop: Gnome
 * Package Manager: DEB
 * Description: Debian is one of the oldest and most reliable distributions. Many distributions are based on Debian and it has one of the largest software library.
 * Screenshot:
 * Website:

Fedora 11

 * Difficulty: Beginner/Intermediate
 * Desktop: Gnome
 * Package Manager: RPM (yum)
 * Description: Fedora is a general purpose distribution that was created by Red Hat.
 * Screenshot:
 * Website:

OpenSUSE

 * Difficulty: Beginner
 * Desktop: KDE
 * Package Manager: RPM
 * Description: OpenSUSE is a Novell sponsored distribution that aims to make itself the easiest to use and most popular distribution.
 * Screenshot:
 * Website:

Slackware

 * Difficulty: Advanced
 * Desktop: KDE
 * Package Manager: TGZ
 * Description: Slackware is one of the oldest and most reliable distributions. It can serve nearly any operating system need.
 * Screenshot:
 * Website:

Ubuntu 8.04 LTS

 * Difficulty: Beginner
 * Desktop: Gnome
 * Package Manager: DEB
 * Description: Ubuntu is the most popular distribution. It is easy to use yet extremely versatile.
 * Screenshot:
 * Website:

31 Flavors of Linux (Plus 4)