Gnome (http://www.gnome.org) is a Desktop and Session Manager. Sawfish (http://sawmill.sourceforge.org) is a Window Manager. KDE (http://www.kde.org) is a Gnome alternative and WindowMaker and Enlightenment are alternatives to Sawfish.
The LBX (Low Bandwidth X) server extension is useful for increasing the responsiveness of remote X applications. Remote Emacs windows are now being delivered to my desktop over a 33 K connection at about 3 times more quickly! (Also more quickly than my LBX connection from MS-Windows/NT using Exceed!)