Two words:
Biblia Clerus!
It was compiled by the Vatican Congregation for the Clergy. It’s a verse-by-verse commentary (or at least passage-by-passage) on the entire Bible. It gives you links to the writings of the Early Church Fathers as well as Magisterial documents that make reference to whatever passage in Scripture you are looking for. It’s the Bible study tool
par excellence. And best of all, it’s free!
Here’s a thread with more info on it:
forums.catholic-questions.org/showthread.php?t=204572
The
St. Paul Center for Biblical Theology also has six excellent
online Bible studies.
Another great resource is
Welcome to the Catholic Church. It has the RSV and NAB versions of the Bible, the
Catena Aurea (verse-by-verse commentary on the Gospels by the Early Church Fathers), as well as the Catechism, documents of Vatican II, most papal documents from the last 100 years, the Summa, the Code of Canon Law, etc., etc. It’s all fully searchable and interlinked (i.e., if the Catechism quotes Matthew 16:18, you click on the footnote and it takes you to Matthew 16:18). It’s great!