Christian Book Distributors is offering Al Mohler's Atheism Remix: A Christian Confronts the New Atheists for just $3.99 until today. The "new atheists" are those in the mold of Richard Dawkins and Christopher Hitchens who have received a lot of media and popular attention lately.
Also, every week Presbyterian & Reformed Publishers gives a super bargain offer for surplus or imperfect stock. Right now you can find the following titles on there. Keep in mind that these are obviously first-come first-serve.
- John Williamson Nevin: High Church Calvinist by D.G. Hart - All of the volumes in this American Reformed Biographies series are good but this one is particularly interesting in focusing on Nevin. Nevin has written what I think is one of the best works on the Lord's Supper and did a great deal of work on the importance of the means of grace authorized in Scripture.
- Calvin in the Public Square: Liberal Democracies, Rights, and Civil Liberties by David Hall - This is an extremely helpful book just for the opening section that surveys prior Christian thought on church and state and the other Reformers leading up to Calvin.
- Justification and the New Perspectives on Paul by Guy Waters - This book is pretty academic but it is a great response to the New Perspective theology as Waters did his doctoral work at Duke under E.P. Saunders and N.T. Wright and so is very familiar with their work.
- Holy Trinity: In Scripture, History, Theology, and Worship by Robert Letham - This is one of the better books you can find on the Trinity and you can't beat that price.
- There are also several works on their by T.M. Moore and Phil Ryken. I think that these two men are excellent examples of the right combination of pastoral skills and academic rigor and I wouldn't hesitate to say anything that they write is worth the time to read.