baobab is able to scan either specific folders (local and remote) or devices, in order to give the user a tree representation including each directory size or percentage in the branch. It also auto-detects any mounted/unmounted device. A graphical representation is also provided for any selected folder.
A detailed documentation on the program could be read at: http://www.gnome.org/projects/baobab
Fabio MARZOCCA <email@example.com>