KDE http://www.kde.org/

Gnome http://www.gnome.org/

XFCE http://www.xfce.org/

Fluxbox http://www.fluxbox.org/version-0.9.php/

Blackbox http://blackboxwm.sf.net/

ICEWM http://www.icewm.org/

Windowmaker http://www.windowmaker.org/

FVWM http://www.fvwm.org/

Englightenment http://www.enlightenment.org/

Afterstep http://www.afterstep.org/

List of window managers for the 'X' window system http://xwinman.org/