PekWM, PekWM, PekWM PeeeeeeeeekWM :-)
takes less ram than fluxbox and blakbox yet offers true pixmap themes.
has window grouping (tabs), autoproperties, dynamic menus anda powerful keygrabber.
combine it with a few dockapps and some launcher and you have a great looking, lightweight easy to use desktop.
cheers,
Alaa