Catholic apologist sites are common, but true Catholic Bible studies and Bible commentaries are rare. Even rarer are the ones that have free materials available. These are the websites that I have found that offer free Catholic Bible studies and that have been reviewed by atholicculture.net and received the "excellent/green" in fidelity category:
www.agapebiblestudy.com Description: In depth Catholic Bible study that utilizes Sacred Scripture, the Catechism of the Catholic Church, Church and papal documents, Church fathers, ancient Jewish sources, ancient and modern Catholic Biblical commentaries, and historical and archeological information. Completely FREE to the public, no registration needed. This site is by far the most in depth resource on the topics it covers. The author is responsive to personal/individual inquiries.
www.scborromeo.org/bible Description: Bible studies on the Sunday liturgical readings. Excellent!! Completely FREE to public, no registration needed.
www.salvationhistory.com Description: Dr. Scott Hahn's site. Multiple resources, several free online Bible studies, multitudes of resources, and studies/programs available for purchase. This site has a lot of things on it and it is a mixture of free and purchase items. Some caution is necessary since the site does employ some protestant resources.
http://haydock1859.tripod.com/index.html Description: Catholic Bible commentary, following the Douay-Rheims Bible text, that was originally compiled by Catholic priest and biblical scholar Rev. George Leo Haydock (1774-1849). It is dated and contains some archaic language and at times it seems to express some rather harsh opinions concerning Protestants and Jews, but it does provide valuable insight. Therefore some caution is necessary. Completely FREE to public, no registration needed.
http://www.cathtruth.com/catholicbible/ Description: Limited but good. Completely FREE to public, no registration needed.
http://www.icubed.com/~rpoe/bib_std.htm Description: Limited but good. Completely FREE to public, no registration needed.
"To be ignorant of Scripture is to be ignorant of Christ"." St. Jerome