At the recent SharePoint Saturday in Phoenix Arizona, I learned about this free resource from Tom Wisnowski…
“Mastering PowerShell” by Dr. Tobias Weltner, PowerShell MVP is available for free download at PowerShell.org/Mastering-PowerShell.pdf. It is a 567 page PDF book. There are lots of other resources on the PowerShell.org site, check it out SharePoint admins.