An important part of book buying for a useful personal-theological library is the purchase of commentaries. This part of the book buying series will come in two parts. First I will touch on a couple commentary surveys that orient the researcher to the best available commentaries for each book of the bible, and then give a couple principles I live by when buying commentaries, as well as some other misc. things.
Three important commentary surveys are available that I find helpful. First, there are the well-known surveys of Tremper Longman on the OT and D.A. Carson on the NT. A couple comments on these two.
Longman's, of course, covers the OT. He rates the commentaries by a star system (out of 5). His comment on each commentary is helpful and very organized (as in, a paragraph for each commentary). At the end of his survey he gives a list of all the 5 star commentaries. Unfortunately, the list of 5 star commentaries leaves out some OT books, so the list is not really a quick reference to the BEST commentaries for each book, but simply a list of the BEST OT commentaries. But in the end a great reference.
Carson's covers many more commentaries than does Longman's, but organization is lost. His blurbs on each NT commentary can range from a couple words to a couple sentences all jammed into large paragraphs, per se. It is hard to quickly reference this survey due to the scattered nature of it, but the fact that he covers so many commentaries and over such a wide range of time makes the organization a thing one could get over for the wealth of information provided. Also, Carson, unlike Longman does have a quick reference at the end of his survey with the best 1-3 options for EVERY NT book. Very helpful!
At this point, I would not buy these surveys because they have both been out for nearly 6 years (an update). They are a bit dated - sort of - and hopefully more updated volumes will appear soon. I bought both in 2008 and I have used them a ton! Thus, they are helpful, but it is probably wise to wait for the next editions and use the library's copy for now, unless you can pick them up on the cheap.
Finally, Jon Evans, has a helpful commentary survey that covers the OT and NT, and combines the best of both worlds of Carson and Longman, and more. He covers many commentaries, is organized, has helpful comment on each resource, and best of all, he updates this survey often. The last edition was 2010. Of course, it is easy to notice he is no Carson or Longman, but many like Donald Hagner, C. Bullock, and Gary Burge give his reference a thumbs up.
These would be places where I start when finding a commentary for research.
Others Book buying posts: