Short for Joe's Window Manager

http://joewing.net/programs/jwm/

Debian is quite a bit lighter by default than Ubuntu and you could do a command line install and then add in the x components you want specifically (you could do that in a lot of distributions really, but Debian has the lightest base install that I feel is absolutely complete.)

As far as window managers go, blackbox (or derivatives), xfwm4, windowmaker (or similar), icewm, evilwm, etc.

If you're talking desktop environments there are really only 3 choices... KDE, Gnome, and Xfce... there are some less known ones but I've never run them and don't know anyone who has... successfully (rox, lxde).

If you prefer a gui similar in functionality to screen but in X then you can always run ratpoison or stumpwm... then there's always sawfish, etc, etc, etc...

There are literally dozens and dozens of window managers.