I've tried a dozen window managers for weeks at a time. For over a decade I always returned to my old reliable WindowMaker. In the past couple years I started using Metacity (default in Gnome now). All I care about is having separate workspaces and a few keyboard shortcuts. I have 7 work spaces: Main (local terminal), Browsing (Chrome/Firefox), Communications (Pidgin/XChat/Skype), Development (GVim/terminal), Email (…
I especially liked docking applications/icons, its good support for virtual desktops and especially the many wmXXX applications that did one job well, in the space of a 64x64 pixel tile.
These days, I mostly resort to the "standard" gnome desktop with whatever it uses and resort to something very lightweight such as fluxbox on resource constrained machines.