Top 5 Commentaries on Every Book of the Bible

Here is one respected scholar's opinion.

I built my first commentary set by author rather than series, trying to find the best commentary on each book. So I took a list similar to this one, which was presented by Tremper Longman III and D.A. Carson. I still think purchasing the "authority" on each book is the best approach for preachers/teachers starting out, and especially for those with a limited budget. Keith Mathison's list seems to be a good place to look as you build your own library for the purpose of preaching God's inspired Word.