Joukuu is a free download for Windows that allows you to manage your cloud based files in one file manager. It will manage Google Docs, Dropbox, and Box.net files all in one window on your desktop.
It syncs Google Docs and Box.net files to your desktop and allows you to even edit them using Office or OpenOffice. It gives you a nicer interface for managing your Dropbox files.
You can even manage folders for each account through the desktop interface.
It is currently in Beta, but appears pretty solid so far. If you use those services and Windows, this is a nice app to use. The site mentions that Sugarsync is coming, so maybe we'll see even more services supported. That would be nice, to be able to manage all the different cloud services from one app.