With new versions of several distributions such as Ubuntu, Fedora, Mandriva, etc., the Linux Distribution Guide available at LinuxLinks.com was updated just in time for those who are planning on exploring Linux. The guide provides a list of features that one should consider when selecting a distribution, e.g., commercial or non-commercial, general or specific purpose (ex. Edubuntu), and server or desktop-oriented.
Frankly, it is always best to try out each one. I did go through the same thing starting with Slackware, Red Hat, Mandrake (now Mandriva) and now Ubuntu.
Happy hunting!