If you write scripts on Windows systems, you should definitely already have the TechNet Script Center bookmarked as they have a huge amount of high quality resources for the full range of Windows admin scripting technologies (as well as the fun of the Scripting Games). Their PowerShell Script Center is a great hub of links and free tools, articles and tips and should be one of the first stops you make in learning PowerShell.

Two of the more comprehensive resources on Script Center have just been updated:

The Windows PowerShell Owner's Manual, which has previously had chapters on Getting Started, Customizing the Console, Shortcut Keys, Piping and the Pipeline and Running Scripts, has had two additional chapters published - The Windows PowerShell Profile and Windows PowerShell Aliases. This is great material, written with the trademark humour of the Scripting Guys and well worth a read.

The second updated resource is The VBScript-to-Windows PowerShell Conversion Guide. If you're already a fluent VBScript scripter and want to update your skills to PowerShell then this is a useful reference, although I think from the PowerShell purist's point of view it probably isn't the best way to learn PowerShell since there's a paradigm shift that translating VBScript directly doesn't take advantage of. That said, if you know how to do something in VBScript and you want to know how to do it in PowerShell, this is the place to come.

The Conversion Guide has been expanded from just VBScript Commands, with new sections covering Dictionary Object Methods and Properties, FileSystemObject Methods and Properties and Windows Script Host Methods.