I've been working with PowerShell for a good while now, but for the millions of people who haven't dipped their toes into it, where should you start? I posted a list of resources back in March, but as of writing this in December 2009 there are loads more great resources to help you get up to speed. All of the items that I'm listing here are free too!
It doesn't do any harm to do a bit of reading before diving in to PowerShell and these are great places to get some background and start learning. The first one is a great book from Sapien Press - since they're releasing a PowerShell 2.0 edition of this book, they've made the PowerShell 1.0 edition available as a free download, which is very nice of them since most of the content is still very relevant in a PowerShell 2.0 world!
In PowerShell TFM, Don Jones and Jeff Hicks (both PowerShell MVPs) cover a lot of ground from the basics to some pretty advanced uses of PowerShell, with plenty of examples that can make you productive right away. I was recommending the 1st edition two years ago and it's still as good today for someone starting out.
Another MVP, prolific author and all-round good guy, Dr. Tobias Weltner has also published a free ebook on his excellent site, PowerShell.com, where you will also find video tutorials and a rather good PowerShell tip of the day. You can either read the chapters online, or download the whole book as a PDF file:
Microsoft's TechNet Script Center has a load of resources for learning and using PowerShell (including a Getting Started Guide). Although it's not as comprehensive as the two ebooks above, you should take a look at their Windows PowerShell Owner's Manual.
I also mustn't forget the original free PowerShell ebook by Frank Koch of Microsoft Switzerland.
Many folk will advise you to just start to use PowerShell in place of cmd.exe to gain hands-on experience (because most of the stuff you do in cmd.exe will work in a similar way), and that's a pretty decent approach, although I would suggest checking out one of the ebooks first. If you do want to dive in at the deep end and try to swim though, I'd recommend you print a PowerShell cheat sheet and pin it up somewhere near your monitor so you can quickly refer to it.
PowerShell Cheat Sheet (by Ben Pearce)
Refcardz PowerShell Cheat Sheet (by Bruce Payette)
PowerShell 2 for Dummies Cheat Sheet (by Steve Seguis)
PowerShell 1.0 Desksheet (by Mike Fourie)
And, if you have a specific requirement for using PowerShell with...
Active Directory PowerShell Quick Reference (by Jonathan Medd)
PowerCLI Quick Reference Guide (by Alan Renouf)
There are two popular podcasts dedicated to PowerShell, one from the US and one from the UK. The PowerScripting Podcast, presented by Jonathan Walz and Hal Rottenberg, is nearly up to 100 episodes as I write this, so they've covered a lot of ground. Jonathan Medd and Alan Renouf have put out 14 episodes of their Get-Scripting Podcast to date.
Since both podcasts started out at a low level and are now somewhat more mature in their PowerShell coverage, I'd suggest listening to a recent episode of each and then going back to earlier episodes and working forward.
If you're into listening to podcasts (like I am), or if you have your first taste with these and decideyou want to try more, you'll find that other tech podcasts do cover PowerShell from time to time, like Show #190 of Scott Hanselman's excellent podcast, which is definitely worth a listen.
Join a User Group
There are a rapidly growing number of PowerShell user groups and script clubs popping up around the world. Don't worry if there isn't one close enough to you; some groups do online meetings, so you can see the presentations from anywhere, and you certainly don't have to be a proficient user to join a user group. I'm trying to maintain a list of the groups on this site.
That's just a few pointers for getting started with PowerShell in December 2009. You'll find loads of people blogging about PowerShell (including the PowerShell Team). There are lots of example scripts available from the TechNet Script Center, and elsewhere. If you're on Twitter, just asking a question that includes the word "PowerShell" will usually result in a response from an MVP or some other enthusiastic PowerShell user, and if you can't fit a question into 140 characters, you'll also get good responses on the official PowerShell newsgroup.