I was a staunch Fluxbox supporter until I discovered Compiz and Beryl. Especially Beryl. This XGL/AIGLX stuff is quite simply 100% epic pwnage. Just to mention some of the features:

Scale (the Expose clone) -- keeping an eye on things, dragging & dropping files and killing apps has never been so easy
Negative Windows -- looking at a screen has always been like staring at a torch (black text, white background). Not anymore -- now even my parents will sit down and read at the computer for more than 5 minutes
Zoom In/Out -- Now even my Grandma will sit down and look up stuff on Google!

The videos on youtube.com don't do it justice. You just have to try it out for yourself (took me about 15 minutes to get it working in Ubuntu).

Once you've installed it, learn the basics, go to a hotspot or (even better) campus and watch potential Linux users flocking around you in no time, while distantly the faint wailing of an Apple fanboi can be heard (What, that guy's $550 craptop out-does my shiny $1100 Macbook with a free download???) Win!!

xfce... sorry

Windowmaker almost exclusively for me. I also, on occasion, enjoy the simplicity of RatPoision and TWM. Using Windowmaker's "wmsetbg", it allows me to set a desktop background for those wm's too. It takes a text-loving person to enjoy my system sometimes. Take a look at my TWM desk-shot, I think you'll get a kick out of it:
http://www.revqueue.com/MYDESK1.jpg


The music player, the IM client (naim), the browser (for the fun of the screenshot) all console based goodness with the exception of the genesis emulator, the transparent xlogo with ye' old wmcube inserted in the center. You'd be amazed at how complex simplicity can be
This screenshot is super-old for me, I should probably take a new one lol.

In short; go simplicity!
--Queue

While I usually use Xfce 4.2 and now 4.4, I have been very impressed with the efficiency of Ion2 and Ion3.

I am very happy with JWM!

fluxbox has always worked great for me. I've had programs that would not run because KDE and Gnome would take up too much of my system's resources. Switching to fluxbox seemed to free up enough resources that the programs would run at a usable speed. Metacity was nice, but I'm a huge fan of the transparent aterm and fluxbox setup.

XFCE is often my second choice on my *nix boxes.

I still have quite a few of the listed environments to try out.

definetly beryl, i'v become addicted when i saw that beauty

I second that!
The latest svn version is very nice with gradients and all the while remaining very small and fast.
But if I have to choose one that is listed... I say Fluxbox. I has eye candy while remaining fairly small and fast.

i've been using fvwm2 for most of the year, recently the fvwm-crystal modification.

beryl&KDE. I like beryl.

Compiz because it's 3D but rock stable.

Blackbox, only because I found it on Windows first and liked it well enough to slap it on Slack. The number of posts about Fluxbox, Beryl and others make me want to give them a shot.

I wonder if there's a liveCD out there with a bunch of these configured so you could try them all? Kinda like screeners for the Academy Awards or something like that.

I have Icewm, Fluxbox and JWM installed and I like all three, but I keep going back to IceWM.

Fluxbox-4-Life!

See ya