Window Maker Desktop: Lightweight Linux Minimalism
Window Maker is a fast, lightweight window manager based as closely as possible on the look and feel of the NeXTStep interface. (You may be familiar with NeXTStep an ancestor of Mac OSX, although the look and feel has changed a fair bit between the two.)
Install it with the wmaker package in Debian or Ubuntu, which provides the current stable version (0.92); or download it from the website if you prefer. As per my article on Xfce, your login manager should have a 'sessions' option that you can use at login to set your session choice.
My very first impression was that it starts up blisteringly fast, even on my low-powered machine. There's minimal screen furniture on startup – no menu bar, just a couple of icons in the top right corner and one in the top left.
The look is initially a little blocky, and seems almost too sparse, but I very rapidly got used to it.
Double-clicking one of the right-hand icons (the Dock) will fire up (in order from the top) an "About" screen, an xterm, and the WPrefs configuration editor. The three little dots in the corner of the xterm and WPrefs icons mean that these are programs which can be launched. You can if you prefer drag the Dock over to the other side of the screen.
One slight annoyance that I noticed is that once you've clicked on the xterm icon and got an xterm up, the icon is then greyed out, and you can't click on it again to launch another xterm. You can use Shift-Ctrl-N to bring another one up, but this doesn't work across workspaces (see below). The only way I could find to get an xterm on another workspace was to right-click on the title bar of the xterm and use the "move to" menu option.
The left-hand icon is the Clip, which acts as a dock extender and can be configured per-workspace. If you have "Automatically create new workspaces" set in the Workspace Preferences tabs of WPrefs (see next section), you can click on the arrows in either corner of this icon to move workspaces. You can also right-click to change various settings.