FreeCommander is a tool that expands upon the usual Windows Explorer interface. With just a little time using this program it is likely that many people will find it very cool and quite helpful. It is not only versatile when managing Windows files, it is also free of charge and very user-freindly.
What FreeCommander looks like
FreeCommander is the work of Marek Jasinski, and much more info can be found on his website here.