Laurie Blank, the director of Emory Law School's IHL clinic, writes in with the following comments on Henry V and the law of armed conflict:
I just saw your post about Henry V and LOAC. The play is indeed saturated with LOAC and jus ad bellum and the application of the legal mores of the period. One clarification---in response to word that the French have launched new attacks on his forces (after he thought he had won the battle), Henry V actually orders his men to kill all the French prisoners they have captured and are holding behind the lines at the Battle of Agincourt; that is when Fluellen exclaims that such conduct is expressly against "the law of arms." Couldn't have a better statement of the prohibition against denial of quarter!
As far as your question regarding whether there are other works, the answer is unequivocally yes. Shakespeare's plays are replete with LOAC issues and references, from Richard III to Antony and Cleopatra. The best treatment of this is in two books by Judge Theodor Meron, written when he was teaching at NYU: Henry's War and Shakespeare's Laws and Bloody Constraint. The latter addresses a wide range of LOAC and other international law issues in a topical framework and incorporates a large number of Shakespeare's plays. Much of Shakespeare's legal analysis tracks closely the treatises of the time: Gentili, Christine de Pisan, Vittoria, Suarez and others. (Side note: I did all the research and editing for the later volume, Bloody Constraint, when I was a research fellow with Judge Meron at NYU, and had the great fun of combing through all the medieval treatises and finding the LOAC norms and interpretations applicable during the time Shakespeare wrote; and doing a small bit of writing on the topic myself). A look at Sheakespeare's plays with an eye to the LOAC issues and questions that arise gives a really fascinating lesson in just how long and deep LOAC's pedigree is---obviously dating back well before the Bard's time. Just as an example, the treatment of Qaddafi's body after he was found and killed in October 2011 harkens back to the famous scene in The Iliad where Achilles drags Hector's body around and around; Homer is clearly quite critical of this conduct. (For more on this, see an op-ed I wrote at the time---on Qaddafi's death, not Hector's).
With respect to Laurie's clarification, I have always read the scene very differently, and certainly, contemporary directors do. That said, she may well be correct as to what Shakespeare was criticizing. The sequence of events in the text is, on closer inspection, very murky. At the end of Act IV, scene 6, Henry orders the killing of French prisoners. In Act IV, scene 7, Fluellen criticizes the killing of "poys" (that is, non-combatant support staff) and "luggage" as expressly against the laws of war. And then Gower explains that "boys" (presumably English boys) have been killed and the King's tent raided---and that he ordered prisoners slain in retaliation. Henry himself then enters and declares that he was not previously angry, but that no prisoner shall receive mercy at English hands now---and he reiterates his order to kill prisoners. I certainly yield to Laurie's reading as to what Fluellen is criticizing, with the sole caveat that I have never seen the play staged to reflect that reading. See, for example, Kenneth Branagh's famous 1989 movie (the relevant portion starts at around the 3:45 mark):