I recommend anything by Nabeel Jabbour or Phil Parshall. Dr. Jabbour is an Arab Christian who grew up in Lebanon and was a missionary in Egypt. He now travels the country holding seminars on Islam and is a good friend and former professor of mine. Dr. Parshall is also a former professor of mine, but is also one of the leading scholars on Islam in the Christian world. He is a former missionary to Bangladesh and the Philippines and has extensive experience among Muslims. I do not recommend books by either Robert Spencer or Ergun & Emir Caner. They are not helpful in understanding Islam at all and take an extreme right wing Christian religious approach in dealing with Islam. The books I have named are ones I have used in classes and take a much more balanced approach to Islam. Samuel Zwemer wrote numerous books and articles which are very helpful. Both Answering Islam (link above) and the Zwemer Center have full books and articles. In fact, the Zwemer Center has a huge collection of Zwemer's books and articles available on the campus of Columbia International University (CIU). The Zwemer Center (insert shameless plug here) also offers courses and seminars in Islam. You do not have to be a student at CIU in order to take a seminar. The seminars only cost $190 and are offered 5 weeks during the Summer and 2 weeks during the Winter. Be sure to check out their website for more information. If you do have questions about a book I listed or a book you found, please ask and I'll try to answer as best I can. I surely hope this helps you in learning how to minister to our Muslim neighbors.