Biblical Training is now offering Bryan Chapell‘s “PR 600 Preaching” course for free (29 MP3s). (The link to the preaching course may not work for you since you need to create a user name and log in to view it.) These are lectures he gave at Covenant Theological Seminary, where he serves as president and which offers many other courses on MP3 for free. Chapell’s books include Christ-Centered Preaching: Redeeming the Expository Sermon.