The Crusades more than any other event in history poisoned Muslim attitudes towards Christians. Christians committed terrible atrocities, particularly in Jerusalem during the First Crusade when Christian Knights rode through the streets slaughtering men, women and children with abandon. The bloodshed was so severe that the Knight's horses often lost their footing.
Muslims frequently referred to the Crusaders as "Franks," or "Trinitarians." Some believed that their presence in Islamic Lands was actually God's punishment because of their sins. One Islamic cleric known as al-Salami said of them
Drive away insignificant things and sluggishness and go to fight the Jihad with your wealth and yourselves. The Franks acted as they did because of the Muslim's blame of God. He warned you with a punishment the like of which He did not warn you with before...If only you would desist from sin! Otherwise he will make you fall into the hands of your enemy....May God hasten your awakening up from the sleep of neglect.
Even modern Christian-Islamic relations are affected by the Crusades. President George W. Bush referred to the War on Terrorism as a "Crusade." Osama bin Ladin seized upon this statement and frequently accused the United States of leading yet another Crusade, and referred to that country as "Crusader America."
An excellent resource you might consider isHoly Warriors: A modern History of the Crusades by Jonathan Phillips.