My Catholic Faith Delivered is a premier source for online Catholic content. They are partnered with School of Faith, Ascension Press, Ignatius Press, Midwest Theological Forum and others to provide online courses in some of the leading publications.
Pillars of Catholicism is an outreach of John Paul the Great University. As of right now they are offering free online courses on the Catholic Catechism. This is a great way to study the faith and earn hours toward maintaining your certification.
Many parishes have Lighthouse CD racks. These are great ways to learn the faith while driving, working out, or anywhere you have access to a CD player. Each CD would typically consist of one hour of material for maintaining certification. If they are not in your parish or if you are interested they also have a CD of the month club.