Fluxbox is a lightweight and slick window manager. Unlike the heavy weights, Gnome and KDE which take 15-30 seconds to get up and running, Fluxbox is up and running as soon as you hit the enter key. Its menu and configuration is done by simple files located in the user directory under the name .fluxbox.
One item to note: don't be put off initially by the rather extremely small fonts that are configured for the styles that come with fluxbox. Simply change them from 100's to 120's in the style files and Fluxbox looks as good as any WM could.
Fluxbox has a slick tabbing mechanism for windows. You can combine multiple windows into one window with tabs across the top by simply middle-clicking the tab of one window (and holding it down) and dragging and dropping on the tab of another window. This is very nice for cleaning up a desktop without exiling applications to other virtual windows (it has those too).
Another nice feature is Fluxbox's support for docking applications. Basicially a docking app runs as sort of an icon with minature display or controls. But not like an icon, more like small controls on a walkman (for example) as opposed to a big dial face of a home stereo. Look at some screen shots, you'll see them.
Fluxbox is an amazing piece of software that does not depend on other WMs. It is small, fast and almost a sure thing for pleasing the eye. (Source < 500K)