Though not a substitute for Bible intake, good commentaries on books of the Bible are very helpful resources for grappling with the text, particularly its more difficult sections. Dr. Keith Mathison, author of several books including From Age to Age: The Unfolding of Biblical Eschatology has compiled a list of what he considers to be the top 5 commentaries of every book of the Bible. There are 66 books in the Bible, so that would be 330 commentaries. [If the average length of one of these commentaries is 250 pages, that would be 82,500 pages of commentary material. Wow.]
But don’t be overwhelmed. You don’t have to read every page of a commentary to find it a blessing. Though if you owned just a single commentary, and (along with the Bible) read 2 pages a day from it, you would complete the entire commentary in about 6-12 months (maybe less for a shorter book).