In the US, RedHat is the most popular distro. In Europe, particularly Germany, SuSE is the distro of choice. The "new" SuSE is actually United Linux, an amalagamation of smaller distros. In Japan, TurboLinux seems to be king, if you care.
SuSE *used* to have a demo install; try
http://www.linuxiso.org/
RedHat is the "microsoft" of distros, so you'll have better luck getting drivers or help for it than others.
I haven't played with any of the Fedora core offshoot stuff (free bits after RH9) but I have a little experience with a lot of different distros - I manage all of the non HP-UX systems at HP's OpenView lab in Roseville.