The Proclamation Trust have a free booklet by Sinclair Ferguson called Preaching Christ from the Old Testament.

Here is the bio:

“Preaching Christ is the great purpose of the Christian expositor. But how do we preach Christ from the Old Testament without falsely allegorizing or spiritualising? Sinclair Ferguson shares some principles that will help us to stay [...]

The Ligonier Ministries have just made available free videos of their Holiness of God conference. It includes speakers such as Al Mohler, R.C. Sproul, D.A. Carson and Sinclair Ferguson and even includes Spanish translations!