I've got both the books metioned above.
The one by Peyette is pretty good but I'm only into chapter 2 so its still real heavy on why the decisions were made for the various parts of the language.
The TFM manual is more focused on actually writing code with a bent towards the Primal scripting products; no worries there as they work for Primal.
I found the Monad book good and pretty accurate so far; although I read it last year during a trip to Interop (yeah, I'm a geek...my wife lets me know).
I am an admin and not a programmer so the Peyette book so far has been a little deeper into it that I really care to go. Altough I must admit that his writing style is easy to read and it is interesting to get the backstory on how Powershell came to be.
I also grabbed Microsoft Windows Powershell Programming for the Absolute Beginner. If you don't know the first thing about programming or scripting, this is the one to start with, IMHO.