GNU Midnight Commander
Midnight Commander (mc) is the best file-manager created for GNU/Linux systems as of date. It is fast, efficient, text-based and second to none when it comes to file-management (except perhaps mv/cp/rm in a pure shell).
 NOT GUI
MC is not a GUI program and it is not designed to be used with a mouse. It is designed to be used with a keyboard.
 Manage Those Files
MC is a file-manager as in "program designed to manage your files". It is not a toy program like GNOME's Nautilus or XFCE4's Thunar.
It let's you move those files around, and it does a great job of it.
GNU Midnight Commander is the ultimate file-manager.