XFCE 4.8 Desktop Environment
Although often classed as light-weight, XFCE qualifies as a medium weight amongst the Linux front ends. It's heavier than, say, LXDE or Window Maker but it uses less resources than KDE or Gnome. However, it is a desktop environment rather than simply a window manager, and as such, it comes with a set of associated utilities.
Actually obtaining and installing XFCE 4.8 proved to be a bit of an adventure in itself. At the time of writing, the XFCE devs haven't released any binaries, instead leaving this to the distributions themselves and other third parties. When I looked, all I could find was an Ubuntu 10.10 PPA that was 64 bit only. Compiling from source is daunting as it involves downloading and unpacking a collection of tar files and then building them in a special order. In the end, I installed a beta of Zenwalk, an XFCE orientated distribution. Take into account that I am therefore not basing my observations on plain, stock XFCE 4.8.
Behind the scenes, XFCE has dropped support for some older frameworks such as HAL in favor of GVFS and others in order to offer more modern, comprehensive hardware and networking support.