As a .NET developer,
Windows Powershell is a great way to increase one's productivity.
Whilst the old 'DOS Prompt' is useful for basic text based operations, the new Powershell allows you to work with objects, giving you a great deal of flexibility when dealing with (for example) a list of file objects brought back from an Active Directory query.
To get into it, best
download the free IDE, and check out some of the
basic scripts available on TechNet.