PowerShell is the future of the command-line for Windows. It's most significant feature is the fact that it is built around .Net and is easily extendable by .Net. In fact, you can use reflection to access any .Net object!
It includes the ability to assign alias's to frequently used commands, define functions, and call a number of pre-defined (and very useful) CmdLets (the equivalent of a command-line utility). It also has it's own scripting language including looping and conditional constructs reminiscent of C#.
Another feature I really like is the ability to navigate to non-filesystem drives, such as the registry. This allows you to navigate the registry the same way you would navigate the file system. You can define your own drives based on the drive providers that come with PowerShell (there are a number of them) or you can create your own provider using .Net.
PowerShell has not been released yet (due Q4 2006), however, you can download RC2.