Inspired by Brian Button's presentation at the St. Louis .NET User Group and Scott Hanselman's dnrTV! episode, I'm starting to look into PowerShell.
Scott Dorman had a link to a free introductory PowerShell e-book a while ago.
I haven't actually read the e-book yet, but when I printed it, I noticed a nice PowerShell Cheat Sheet at the end of the book, which looks like it might be very useful.