This Bible contradiction is from the Skeptic's Annotated Bible.
100 Philistine foreskins
2 Samuel 3:14 View context
And David sent messengers to Ish-bosheth Saul's son, saying, Deliver [me] my wife Michal, which I espoused to me for an hundred foreskins of the Philistines.
200 Philistine foreskins
1 Samuel 18:27 View context
Wherefore David arose and went, he and his men, and slew of the Philistines two hundred men; and David brought their foreskins, and they gave them in full tale to the king, that he might be the king's son in law. And Saul gave him Michal his daughter to wife.