Enlightenment DR-16
e16 is a well established window manager released in 2000, is stable and well developed, the most current version is 1.0.1 and was released on 10 September 2009. e16 has a low overhead, is highly graphical, widely theme-able, extremely configurable, yet is an unobtrusive interface.
It runs on pretty much any architecture including windows (not sure 'bout OSX never tryed, but aye on linux on powerpc's) and pretty much any operating system. It integrates easily with gnome & KDE, it's not matched to Xfce but treats it as gnome, plus stand alone applications. Their are also a set of epplets for e16. Epplets are small, handy Enlightenment applets, similar to dockapps or applets for other packages. Nearly all functions of the window manager can be handled without mouse input, including application launching via e16keyedit.
e16 is just " an apt-get install e16 " away. The version in lenny is not the newest on offer, but is fully developed & functional. The version in squeeze & sid is the latest release.
Here are a few screen shots (HINT: click in the images);
Additional themes for e16 are on offer at, Themes for your Enlightenment! (e16).
Enlightenment DR-17
e17 of the Enlightenment window manager represents an evolution into the next generation of desktop environments: the desktop shell. e17 will provide integration between files and your environment in a seamless manner while encompassing a graphically rich and flexible architecture. It will not compete with gnome or KDE, but be a completely new way of visualizing your desktop, based around the Enlightenment Foundation Libraries (EFL) which was built from the ground up for this task.
Still in heavy development, several applications that will be part of the e17 release and examples of what is possible are already available in SVN, such as Entice, Entrance, and Evidence.
Here are a few screen shots (HINT: click in the images);
Bling Bling_______A custom background I did for Freespire
OzOs Default

Some useful e17 sites;
Enlightenment
eXchange
e17-Stuff.org
Shameless self promotional plugs
OzOs the reality different
CafeLinux Forum
Debian & Enlightenment
debe17
e17 is on offer for sid via APT and it's fairly up to date and newer then the one in experimental. Since e17 is still under development and is not even considered at the alpha stage (in other words it's ustable) building from source is still recommended. Although if one just wants to have a look at it & give it a test ride the one in the repo is easier to install. For those whom might be adventurous, I've a wee How To, The Optimum OzOs Experience on Debian GNU/linux.
Cheers