All of the month of lunches are great books especially if just starting out. Something else that helps (while doing the books) is pick something that you need to do at work – an issue/problem that comes up – and commit to doing it through PS. This in combination of the books is something great to go through and really reinforces the ideas taught in the books.
I know you asked for books, but I liked watching all the Jeffrey Snover videos about powershell that are online. He's in inventor of it, and it's nice to hear his intentions behind it, and what he thinks is cool about it.