The God of Bible vs. the God of Qur'an
The Character of God in Bible and Qur'an (Notes from a Muslim-Christian dialogue in December 1998)
Samuel Zwemer's classic: The Moslem Doctrine of God
The Only True God
Is Allah the God of the Bible? (several somewhat differing perspectives)
The cry of the Heart for God – A Comparison of Mysticism and Intellect in Saint Augustine and Al-Ghazali
"God is one", some book excerpts: [*], [*]
On other sites:
The Attributes of God
Survey of Bible Doctrine: God
Our Mysterious God
The Pursuit of God by A. W. Tozer (a classic): 
Why God Became Man
Who is Jesus?
How to Please God: Faith or Works?
Answering Islam Home Page