This is a series of three window managers. BlackBox is the original, Openbox and Fluxbox are forks.
BlackBox is comparable to JWM, and loads in about 3MB of memory.
Openbox is rarely used stand-alone, it is however the window manager of choice in a number of other desktop environments such as Gnome, KDE and LXDE. It runs in about 7MB of memory. CrunchBang is and example of distribution based on Openbox.
tint2 is a simple panel/taskbar made for modern X window managers. It was specifically made for Openbox but it should also work with other window managers (GNOME, KDE, XFCE etc.). It is based on ttm http://code.google.com/p/ttm/