Here's a very popular X Windows interface setup - GNOME:
http://www.gnome.org/seegnome.html
Keep in mind that one of the beauties of windowed desktops in Unix and Unix-like systems is that there is no set shell (excepting the default of CDE on commericial unices [AIX, Solaris, HP/US (I tihnk)]). Linux and FreeBSD ship with Gnome (pictured in the link above) or KDE (
http://www.kde.org) as their default desktops. However, you do not have to use any of these - there are all sorts of window managers out there. To name a few:
Blackbox
Enlightenment
fvwm
Icewm
The list seems endless. Check out
http://www.themes.org/ for more beautiful examples of XFree86 desktops in action.