And yet another tool I recently came across: xplorer². It is meant as a replacement for the Windows standard File Explorer or “Verkenner”. Difference: ability to use dual panes, totally customizable (the toolbars, columns, panes, etc..), several handy buttons are available for the toolbar like the Run command, DOS box, preview. The lite version is free, and you can even do batch operations on files (mass rename with tokens).
A nice extra is the calculation of subfolder sizes, which is unavailable in Windows Explorer. This can be set to automatic, or you can add a button (“measure”) to do it manually (which, of course, takes the load off your system).