Eat your heart out, Windows Explorer. This powerhouse file manager beats the pants off Microsoft's built-in utility on almost every count. Start with the interface: Xplorer2 lets you browse two or more folders in one window using panes (as in Total Commander or FAR) and tabs.
You can save several window layouts and quickly switch among them when necessary. Visual filters let you more easily navigate overcrowded directories. Selecting several files is a breeze, since you don't have to hold down the Ctrl key. Xplorer2's tweaks aren't limited to the interface, either. You can rename multiple files at once, split and merge files, synchronize folders, and shred data to prevent recovery.
The program supports NTFS hard links (which are more powerful than shortcuts, allowing you, for instance, to move the source file without breaking a link). An enhanced DOS command line lets you create scripts for processing file batches. All in all, there's a good chance you won't go back to Windows Explorer once you get a look at Xplorer2.