From a defender's standpoint your best bet is Niccolo Barbaro's "Siege of Constantinople". Although while reading this you have to take into account the extreme bias that Barbaro writes with. A Venetian physician by trade, he did not care for the Holy Roman Empire and makes no attempt to hide his disdain for the poor defense of the city. If you're looking for a more formal account of the days during and after the Siege, Steven Runciman's book, "The Fall of Constantinople" gives a very accurate timeline of Mehmed's arrival in the city and the actions he takes to quell the violence.

Sources:

Runciman, Steven. The Fall of Constantinople 1453. New York: Cambridge University Press, 195. http://books.google.com/books?id=CJz8BCdxlfEC&printsec=frontcover&dq=runciman&hl=en&sa=X&ei=3P2bUtmENcfxoATJ_YKoAg&ved=0CC0Q6AEwAA

Barbaro, Niccolo. Siege of Constaninople