KDE 1.x (what more do you need I've seen it on machines with 16MB)
KDE 3.5.x (more than you'll ever need... yet doesn't fit in 640k)
Enlightenment 16 (snazzy and decent... sadly programmed by lunatics)
LXDE (what I use when I can't have the above)
That pretty much sums it up... I've used dwm on my Fujitsu P1120 which was as much tiling as I could cope with, as well as JWM and IceWM on occasion with a stint of running the ROX desktop... I still love that file manager.