IceWM

From Grokdoc

IceWM is a window manager with a small memory footprint with an appearance and handling quite similar to what the average user is accustomed to from the products of a big software company in redmond.

It has few dependencies and is very themeable, though not as configurable as other windowmanagers. It has no built-in support for applets, but already features a mailchecker and a clock within the taskbar.

IceWM can be found at http://www.icewm.org.