This is a pretty popular topic even for academic historians, so there are a lot of books! Here are some important ones:

Secondary sources:

Michael Angold, The Byzantine Empire 1025-1204: A Political History (Longman, 1984) - for the background to Byzantine politics

Jonathan Harris, Byzantium and the Crusades (Hambledon and London, 2003) - this is about the relationship between the empire and the crusaders in general, leading up to the events of 1204

Donald E. Queller and Thomas F. Madden, The Fourth Crusade: The Conquest of Constantinople, 2nd ed. (University of Pennsylvania Press, 1997), and

Jonathan Phillips, The Fourth Crusade and the Sack of Constantinople (Pimlico, 2005) - Queller/Madden and Phillips are probably the two best histories of the crusade. (I prefer Phillips' book, which is more recent and more detailed)

There are also lots of primary sources that have been translated into English:

O City of Byzantium: Annals of Niketas Choniates, trans. Harry J. Magoulias (Wayne State University Press, 1984) - Niketas is the key Byzantine eyewitness to the crusade

Joinville and Villehardouin, Chronicles of the Crusades, trans. Carolina Smith (Penguin, 2009) - Geoffrey de Villehardouin is the main crusader account. For some reason it's traditional to bundle him together with Jean de Joinville's account of the later Seventh Crusade. M.R.B. Shaw's translation from 1963 (also from Penguin) would also work if it's easier to find, but Smith's is better.

Robert of Clari: The Conquest of Constantinople, trans. Edgar Holmes McNeal (Columbia University Press, 1936) - Robert is the other main crusader account

Alfred J. Andrea, ed., Contemporary Sources for the Fourth Crusade (Brill, 2000) - this is a collection of other accounts of the crusade from various perspectives

I've mentioned all of these just to show that there's a ton of stuff out there. But in my opinion, the first book you should start with would be Jonathan Phillips.