1. The Knights of Columbus offer two free online courses and a free correspondence course in the Catholic faith. Course booklets are also available online at no cost.
2. John Paul the Great Catholic University provides a free online course entitled “Pillars of Catholicism” taught by Dr. Michael Barber, Dr. Christine Wood, and Fr. Andy Younan.
3. The St. Paul Center for Biblical Theology offers several free online Bible study courses in text and audio forms, including “Covenant Love: Introducing the Biblical Worldview”; “Genesis to Jesus”; and in-depth courses on several books of the New Testament. This site also contains an excellent resource library.
4. The Catholic Home Study Service provides free classes about Catholic faith, life, and prayer.
5. If you don't mind paying a bit for a class, Catholic Distance University has some excellent options for courses and seminars; the University of Notre Dame's STEP program offers the opportunity to earn certificates in various areas of theological studies; Catholic Courses through TAN books is always adding new classes for reasonable rates; International Catholic University also provides quality classes for reasonable prices, and of course, Franciscan University of Steubenville has a top-notch distance learning program with MA degree and non-credit options.
6. Coursera teams up with colleges and universities to offer courses in a wide variety of subjects. There's something for everyone here. Classes are free, but certificate options are also available for reasonable prices.
7. Like Coursera, edX offers college level classes in nearly ever subject area. Classes are free, but certificate options are also available for reasonable prices.
8. The Open Culture website lists over 1,000 free courses, some on iTunes, some on websites, and some on both, from colleges and universities like Stanford, Berkeley, Yale, Harvard, and many more. The site also offers links to free online language lessons and free online textbooks.
9. The Annenberg Learner site hosts plenty of fascinating video series for learners of all ages.
10. Don't forget iTunes U for a whole bunch of interesting, free classes.
11. Check out the open courseware pages at colleges and universities like MIT, Yale, Notre Dame, Harvard and others for a wide range of options.
12. For lovers of fantasy literature, don't miss the Mythgard Institute. Mythgard offers paid options to audit classes or earn credits toward an MA degree in Literature and Language, but its Academy section provides several free online courses, focusing especially on the writings of J.R.R. Tolkien. The Tolkien Professor offers further Tolkien classes and information.
I'm merely scratching the surface with this list, but there is enough learning material here to last a lifetime. A word of caution, however... Some of the college, universities, and classes on some of the sites mentioned here are secular in nature and contain ideas that are incompatible with Catholic belief. Be on your guard as you learn. Nevertheless, enjoy your classes and never, ever stop learning!