I like StumpWM. It's a tiling window manager, which I've come to consider vital (I'll never go back to overlapping windows if I can help it). It's also written in Common Lisp, which is a powerful dynamic programming language. I like that I can easily extend my window manager on the fly (I've even been thinking of implementing a terminal within StumpWM, so I can get rid of my current terminal).
It's a little annoying that a lot of stuff assumes GNOME or KDE, but I'm able to get by.
I've heard good things about i3, dwm & exwm. The latter is written in elisp, of all things!
KDE Plasma is generally really solid in my opinion. I installed kubuntu-desktop on my xubuntu install yesterday, and it both looks pretty good and works really well. The whole KDE stack, with kwin instead of mutter and Qt instead of GTK, also feels a bit better engineered to me than the Gnome side of things.
Or, if you're feeling adventurous, i3wm is really nice. That's what I run on my laptop, which is my main programming computer, and I would never again consider running a floating window manager instead of a tiling one for programming.
It's a little annoying that a lot of stuff assumes GNOME or KDE, but I'm able to get by.
I've heard good things about i3, dwm & exwm. The latter is written in elisp, of all things!