If your not yet familiar with the ins and outs of ports you can use xdm as your graphical "Display Manager". It is described in the FreeBSD handbook;
http://www.freebsd.org/doc/en_US.ISO...ook/x-xdm.html
You could also use the Gnome Display Manager (GDM) or Kde Display Manager (KDM). I would suggest XDM or GDM over KDM only because KDE apps including KDM will look some what out of place in and around XFCE. The Gnome apps and GTK in general will look more native in and around XFCE.