The free Logos Book for the Month for December is Exodus: Saved for god's Glory by Philip Ryken. You can also purchase 1 and 2 Timothy and Titus—To Guard the Deposit, Jeremiah and Lamentations: From Sorrow to Hope,1–3 John—Fellowship in God's Family, Job: The Wisdom of the Cross, Hebrews: An Anchor for the Soul, and Matthew—All Authority in Heaven and on Earth in the same series for $0.99, $1.99, $2.99, $4.99, $6.99 and $9.99 respectively. While you are at it, you can register for a chance to win the seven volume Foundations of Evangelical Theology series. For all these offers, go to the Logos' Free Book of Month page here.
To get the commentary The Gospel According to St. Mark by Morna Hooker for free go here.