i3 is a dynamic tiling window manager with clean, readable and documented code, featuring extended Xinerama support, usage of libxcb instead of xlib and several improvements over wmii.
IceWM is a window manager for the X Window System. The goal of IceWM is speed, simplicity, and not getting in the user’s way.
Fluxbox is a windowmanager for X that was based on the Blackbox 0.61.1 code. It is very light on resources and easy to handle but yet full of features to make an easy, and extremely fast, desktop experience.