I've just consulted a medieval historian over lunch.
There isn't one book about the kings. And there were a number of Queens too.
Here's a list and brief account, from Wikipedia:
http://en.wikipedia.org/wiki/King_of_Jerusalem
Try one of these to read more:
Bernard Hamilton, "Women in the Crusader States: The Queens of Jerusalem", in
Medieval Women, edited by Derek Baker. Ecclesiastical History Society, 1978
Bernard Hamilton,
The Leper King and his Heirs: Baldwin IV and the Crusader Kingdom of Jerusalem (Cambridge University Press, 2000).
Zehava Jacoby, “The Tomb of Baldwin V, King of Jerusalem (1185-1186) and the Workshop of the Temple Area”, in
Gesta, 18 (1979), pp. 3-14.
Steven Runciman,
A History of the Crusades, vol. II: The Kingdom of Jerusalem (Cambridge University
A primary source:
William of Tyre, A History of Deeds Done Beyond the Sea. E. A. Babcock and A. C. Krey, trans. (Columbia University Press, 1943).