Knowing God, by JI Packer. A great read for anyone who considers himself a Christian!
Last few reads were also theology: Holiness, by JC Ryle, which I consider one of the all-time best books on the Christian life, and The Westminster Confession of Faith, along with the Larger and Shorter Chatachisms.
It's amazing to me how my mind is so... lax. The Westminster Divines, Bishop Ryle, and Packer all had extraordinary intellects, and their works reflect that God-given intellect. Reading their works illustrates to me my own mental sloth!