Xfce - Xfce is a lightweight desktop environment for UNIX-like operating systems. It aims to be fast and low on system resources, while still being visually appealing and user friendly.
i3 - A dynamic tiling window manager designed for X11, inspired by wmii, and written in C.
LXDE - Why will you like it? Less resource needs. You can use it on your less-pricey embedded board or salvaged computer. Component-based design. Don't want something in LXDE, or you don't want to use LXDE but only part of it?
dwm - dwm is a dynamic window manager for X. It manages windows in tiled, monocle and floating layouts. All of the layouts can be applied dynamically, optimising the environment for the application in use and the task performed.
GNOME - An easy and elegant way to use your computer, GNOME is designed to put you in control and get things done.
Openbox - Openbox is a highly configurable, next generation window manager with extensive standards support.