There are numerous books written about Islam, both pro and con. The "pro" books unfortunately exclude the unsavory aspects of Islam that threaten our nation - as if they don't exist. These are written by Muslims or "politically correct" Islamic sympathizers. I do not list those here. The books I recommend below are those that give the whole story of the subject matter they focus on. Links are provided to Amazon.com so you can read all the reviews as well and get a more complete flavor of each book.
Here they are in no particular order:
Global Jihad - The Future in the Face of Militant Islam, by Patrick Sookhedeo
Europe's Ghosts - Tolerance, Jihadism, and the Crisis in the West by Michael Radu
Surrender: Appeasing Islam, Sacrificing Freedom by Bruce Bawer
The Complete Infidels' Guide to the Koran by Robert Spencer
A God Who Hates: The Courageous Woman Who Inflamed the Muslim World Speaks Out Against the Evils of Islam (Hardcover) by Wafa Sultan
Muslim Mafia by David Gaubatz and Paul Sperry
Defeating Political Islam by Moorthy S. Muthuswamy and Steven Emerson
The Truth About Islam by Robert Spencer
America Alone by Mark Steyn
While Europe Slept by Bruce Bawer
Because They Hate: A Survivor of Islamic Terror Warns America by Brigitte Gabriel
Jesus and Muhammad: Profound Differences and Surprising Similarities by Mark Gabriel
Militant Islam Reaches America by Daniel Pipes
Jihad, Incorporated - A Guide to Militant Islam in the US by Steven Emerson
Terrorists Among Us - Jihad in America by Steven Emerson
Obsession: Radical Islam's War Against the West by Wayne Kopping
Stealth Jihad: How Radical Islam is Subverting America without Guns or Bombs by Robert Spencer
Europe's Ghost - Tolerance, Jihadism, and Crisis in the West by Michael Radu
Religion of Peace? Why Christianity Is and Islam Isn't by Robert Spencer
Islam Unveiled: Disturbing Question about the Worlds Fastest Growing Faith by Robert Spencer
Inside Islam: A Guide for Catholics by Robert Spencer
Islam: What the West Needs to Know by Robert Spencer, Walid ShoebatBat Yeor, and Serge Trifkovic (DVD)
While America Sleeps: How Islam, Immigration and Indoctrination Are Destroying America From Within by Wells Earl Draughon
Infiltration: How Muslim Spies and Subversives have Penetrated Washington by Paul Sperry
The Dhimmi: Jews & Christians Under Islam by Bat Ye'or and David Maisel
Islam and Dhimmitude: Where Civilizations Collide by Bat Yeor, Miriam Kochan, and David Littman
The Legacy of Jihad: Islamic Holy War and the Fate of Non-Muslims by Andrew G., M.D. Bostom and Ibn Warraq
The Legacy of Islamic Antisemitism: From Sacred Texts to Solemn History by Andrew G. Bostom and Ibn Warraq
The Islamic Anti-Christ by Joel Richardson Compares the end times prophecies of both Islam and Chrisitianity. Shows how Islams' Mahdi is Christianity's Anti-Christ and Christianity's Messiah is Islam's Anti-Christ. Talk about polar-opposites!
Another listing of books on Islam listed under vaious categories that may prove helpful is here.
That's the bulk of the best books I am aware of. Please bring others that you believe are worthwhile to my attention.