Islami City
Islami City: Islam History the Rightly Guided Caliphs
Good article on the first four caliphs of Islam. The reign of each is summarized briefly, emphasizing their most important attributes, actions, and contributions to the Islamic community.
Other
Islam 101: Chronology of Crusades
Timeline of the major events of the Christian crusades from 1095 to 1291 A.D.