Recently seminaries have begun putting up a number of their full courses for download. A lot of them are on itunes.
RTS (Reformed Theological Seminary)
Over 40 of their courses are on the itunes site. Highlights: Edmund Clowney and Tim Keller lectures on preaching. Excellent stuff.
Biblical Training (Gordon Conwell)
Aims to provide a complete seminary level education for free. Composed mainly of courses from Gordon Conwell. These are wonderful. Highlights for me were Frank Thielman's New Testament Theology Class, Robert Stein's Gospels class, and Timothy Tennent's Missions class.
Covenant Theological Seminary
Over 30 courses. Excellent quality. Highlights Bryan Chapel's Christ Centred Preaching class.
Westminster Theological Seminary
Highlights include Edmund Clowney on Biblical Theology.
Dallas Theological Seminary