The amazing range of quality window managers and themes that Linux had, compared to other operating systems was what attracted me to Linux in the first place.
The following two sites were my primary portals. Sources of information and inspiration ..
Window Managers for X
loads of information and links to many many window managers and desktop environments for Linux and other X-window systems. Many of them are Sourceforge projects.
Freshmeat: Themes for Linux
Thousands of themes, organised by window manager. Minimalist through to over-the-top bizarre!
RedHat Window Manager Switching Tool.
This tool changes your default desktop/window manager. You need to log off and back on again for it to take effect.
Window Manager exit options.
Many window managers give you the choice (often from a menu) of starting up another window manager in its place. This is one way to change window managers on the fly, but you have no guarantee of being able to return to the window manager you started with.
MultiWM
This is a consul-based utility that displays a menu of window managers at startup. When you choose, it changes .xsessions and .Xclient , then starts X.
WARNING! It will make your emacs and xterm look like this
Note: There are lots of useful sites listed in the DOWNLOAD file with this software. Worth checking out.
Kewl
Kewl is a dynamic switcher, written in Tcl/Tk. Select the window manager of your choice from a menu by double-clicking. That window manager will start, and kewl will iconify itself. If you exit from the window manager, kewl will show itself, and allow you to choose a new window manager.
here are some screenshots of kewl and theWitch running side by side.
theWitch
theWitch is a dynamic switcher, written in Tcl/Tk. Press a button to kill the current window manager and start a new one. theWitch cannot be killed, because a daemon ensures that it is always restarted if it dies. theWitch has been designed to be robust and bullet-proof. It is now themeable.