Linux Display Manager

         1) Use of      2) Choice  3) Choice     4) Customized  5) User
            Xsession.d     of WM      of Locale     Startup        List
  XDM       ++             --         --            ++             -
  GDM       +              +          ++            some alt.      ++
  KDM       --             +          --            custom         ++
  WDM       ++             +-         --            --             -

(128K) LightDM - simple display manager
(204K) xdm


(1.2M) SLiM - desktop-independent graphical login manager for X11
(2.2M) kdm
gdm
enhance
CDM




Reference :
XDM, GDM, KDM, WDM shootout :-)