DE -- LXDE

WM -- IceWM

For low end machines I prefer LXDE which uses Openbox as the WM by default. Personally for me, I only use Openbox with tint2, but for family members they can use LXDE.

Xfce isn't really lightweight these days: in Mint and Fedora, there's little to choose between it and Gnome. I think it's becoming the replacement for Gnome for those who don't like Gnome 3.

For a lightweight environment, I'd go for Fluxbox with fbpanel. But I also have a liking for Icewm, which was the first GUI I ever used.

And I'm back with this setup now, only with Nitrogen instead of Feh to set the wallpaper.

Fantastic keybindings and works with everything out of the box (unlike, say, XMonad, which takes tweaking).

Not as great as Xmonad+DMenu+Xmobar when that setup works, but this works all the time.

I used GNOME 3 for a while and now I am at XFCE and I don't think I am going anywhere (all on Fedora).

I've taken to using mostly LXDE these days, with occasional forays into xfce. I still have a soft spot for good ol' Gnome 2, though.

I've been using XFCE on my desktop and netbook because I do find it a little less intensive than Gnome or KDE. I know what you mean, DavidMcCann, but I still feel gnome and KDE use more resouces, especially video.
For the netbook though I'm reading this thread and taking notes as I would rather something lighter but can't, yet, quite come to terms with no task bar or "system tray" (yes, I know that's Windows talk, sorry it works). I'd be interested in something like ratpoison using opacity though as opacity in XFCE [using the built in compositing] is remarkably tolerable in speed and allows more information on this little screen.

Fluxbox and rox filer and there is nothing negatively utilitarian about it. In fact, if you can write simple scripts its easy to customize and add what ever functionality you want to it.

Enlightenment by far

Though it is considered a Desktop Shell not a full blown Desktop Environment

LXDE

DE: Xfce
WM: Openbox

I've been using Openbox with either xfce4-panel or fbpanel lately. I like Fluxbox and IceWM, too.

xmonad at all!!

I'm using entirely Xfce now, but considering Openbox with a tint2 panel. My only issue with Xfce is Thunar. I just can't seem to like it no matter what I do, so I may swap it out for PCManFM.