I use StumpWM, but it can be a real pain in the ass to get running and configured. I like that it has static layouts: you manually split the screen into panes and windows go in those panes, rather than everything resizing & shuffling whenever you open a terminal. I also really like the keybindings, which are by default all preceded by C-t, so you'd hit "C-t c" to open a new terminal--this avoids the whole "window manager ate all my alt-key combinations" problem you'll run into with i3 and a lot of other WMs. The problem is that it's Common Lisp, so the binary is huge and it takes a long time to start up, and sometimes it crashes in interesting ways. But on the other hand, it's Common Lisp, so you can connect to it from Emacs and play with the code... at least until you crash it.

I'm thinking about trying the new Guile window manager that popped up here a few days back, it looks like it has a StumpWM-esque style and maybe Guile is a little more light-weight/less flaky than most Common Lisp implementations.