Often times, such as in the recent movie Kingdom of Heaven, the Crusaders are presented as imperialists more motiviated by money and greed than by devout conviction. In a recent post I mentioned a book about the Crusades I had recently completed, which did a good job of preseneting the genuine if misguided religious zeal of the Crusaders. It also emphasized that a significant part of the Crusader's perspective was that Islam was invading and conquering Christiain lands.
A couple of days ago, Loren Rosson wrote a post entitled, Understanding the Crusades, which also focused on Crusader motivations. Therein, he concludes that "what motivated them wasn't money or material gain: on the contrary, they dreaded the dangers of travel and expensive costs involved over the trek to Palestine, and there were few rewards to be won in the Holy Lands. Crusaders were motivated by anything but economic interests. They were motivated by sincere religious zeal."
Quoting a Crusader scholar, Rosson also notes that the Crusaders adopted the same policies of tolerance (relatively speaking) that the Muslims had before them:
[W]ithin a decade or two of their occupation of Palestine the crusaders had adopted a policy of toleration, based on the Muslim treatment of subject Christians and Jews. Muslim and Jewish shrines, mosques and synagogues were open. Muslims worshipped even in Christian shrines and churches and there was at least one mosque-church.
It is a fascinating period of time about which there are many misconceptions and few dispassionate commentators.
Update: Rosson has posted a new blog on the issue.