How to manage desktop real-estate for Ubuntu/Gnome
At least Window Maker has widget support built-in (called DockApps). A quick sample(1) can be viewed at Window Maker documentation.
Another choise, if one isn't ready to switch window manager yet, is the Docky(2) frontend for Gnome Do(3) which can be used at least as a dock.
(1): http://www.windowmaker.info/features.php?show=dock-clip
(2): http://do.davebsd.com/wiki/index.php?title=Docky
(3): http://do.davebsd.com/