Here are some books I have found helpful for various reasons. They are not covenantal or presuppositional books per se, nor will you agree with everything in them. Far from it. But they will help you think deeply and critically about theology, philosophy, and apologetics even though most of them are written on an introductory level.
A Shot of Faith to the Head – http://www.amazon.com/Shot-Faith-Head-Confident-Believer/dp/1595554343/ref=sr_1_1?s=books&ie=UTF8&qid=1338582505&sr=1-1
Where the Conflict Really Lies – http://www.amazon.com/Where-Conflict-Really-Lies-Naturalism/dp/0199812098/ref=sr_1_1?s=books&ie=UTF8&qid=1338582587&sr=1-1
Divinity and Humanity – http://www.amazon.com/Divinity-Humanity-Incarnation-Reconsidered-Theology/dp/052169535X