I've gone through a good number of window managers in the past 7 years. I've gone through several cycles of wanting eye candy, then wanting minimalism, then wanting functionality and speed of use. (not necessarily 'ease of use', by most people's definition)
Below is a list of some of the window managers I've tried using, and some thoughts on them.
FluxBox is one window manager I keep coming back to. It's easy to set up (just editing a couple of things in the default configuration usually suffices to me) and widely available. I have a soft spot for BlackBox derivatives, and FluxBox is the one wm that has stayed true to the original BB philosophy in my view. For a long time, though, I didn't like the idea of tabbed windows, but now I've started using them quite a bit as a replacement for wmii's stacked panes.