The decisive loss of the Byzantine army to the Seljuk Turks at the [Battle of Manzikert]? in 1071 brought the beginning of Byzantine pleas for troops and support from the West.
There is an interesting symmetry between the terms "Crusade" and "Jihad". In the West the term "Crusade" has positive connotations (for example a politician might use rhetoric such as "a crusade against illegal drugs") while the term "Jihad" has negative connotations associated with fanatical holy war. In the Islamic world the term "Jihad" has positive connotations that include a much broader meaning of general personal and spiritual struggle while the term "Crusade" has the negative connotations described above. Thus to correctly translate nuances of meaning, the use of "Jihad" in Arabic should be translated to "Crusade" in English while use of the Arabic term for "Crusade" should be should be translated to "Jihad" in English.
In truth much of what the crusaders did was less than heroic. They committed atrocities not just against Muslims but also against Jews and Christians. For example the Fourth Crusade never made it to Palestine, but instead sacked Constantinople the capital of the Christian Byzantine Empire. The Byzantine Empire eventually recovered Constantinople, but its strength never fully recovered, and the Byzantine Empire finally fell to the Ottomans in 1453.
First Crusade
1095 - 1101? The First Crusade succeeded in capturing Jerusalem and establishing a Kingdom of Jerusalem.
-- Adhemar de Monteil -- Albert Of Aix -- Alexius I -- [Peter the Hermit]? -- Amalric I of Jerusalem --Amalric II of Jerusalem
Second Crusade
1145? - 1147 -- Alphonse I
Third Crusade
-- Saladin -- Ambrose the poet
Fourth Crusade
1204 The Fourth Crusade, instead of attacking Muslims, conquered the Christian Byzantine Empire of Constantinople in 1204.
-- Alexius III -- Alexius V -- Pope Innocent III
Fifth Crusade
1217?
Sixth Crusade
Seventh Crusade
Eighth Crusade
1270?
-- Alphonse of Toulouse -- Albertus Magnus
[Children's Crusade]?
1212?
Not really a crusade in the same sense as the others listed above, the Children's Crusade involved thousands of children ranging in age from six to maturity gathered together from all over France and Germany. Operating under the belief that their innocence and purity would allow this army of children to overcome the infidels, they headed for the Holy Land. Many died en route, and the rest were sold into slavery after sailing to Egypt. None reached Palestine.
General links:
Acre, Palestine -- Jaffa?
-- Alphonso VIII of Spain which crusade?