Books to have at your fingertips
There are a couple of books that I have found to be particularly useful. Whether you're a beginner or you have your black belt in script-fu, you'll find them to be excellent references.
Windows NT Shell Scripting is an excellent place to start. Tim Hill does a great job explaining the basics of how shell scripts work, then gets in to some real-world scripts. Many other books on scripting use contrived examples, but his scripts are actually useful.
The Windows 2000 Scripting Guide from Microsoft Press is written with the Windows Script Host in mind, but contains hundreds of useful administration scripts. There are a lot of hidden treasures in there.