This is a very helpful commentary, especially the 40-page appendix on the "spirits in prison" passage. It's not as full as some other commentaries on the actual text itself, (I. Howard Marshall and Karen Jobes both have good, deeper commentaries), but Grudem is still worth getting, especially for a quick introduction to and overview of a given passage.
This is a very good exegesis of 1 Peter. It provides in-depth analysis of the major issues in the text, and it doesn't get bogged down in scholarly discussions. Grudem's appendix on the spirits in prison is worth the price of the book
This is a top-notch commentary on 1 Peter from Wayne Grudem and is just a kind of commentary you would expect from such a top-notch theologian. That said, he doesn't overcomplicate his explanation of the text and despite being very thorough it's a very easy to read commentary. This is probably one of the best in the Tyndale New Testament series and comes at a very reasonable price. So it's well worth having on your bookshelf if you preaching through 1 Peter or leading a Bible study group. Probably one of the best commentaries on the book although Evangelical Press also have very useful one in the Welwyn series which is also worth checking out.