The perfect sacrifice is one which is accompanied by repentance and subordination to God's will (Talmud, Berakhot 23a). (In response to the post below this one, it should be noted that my above answer does not refer to human sacrifice, which is prohibited by the Torah.)
Discussion on the Christian Perfect Sacrifice
Judaism does not agree with Christianity that the "Jesus Sacrifice" was the perfect sacrifice. Judaism fundamentally disagrees with the Christian concept of Jesus' divinity and therefore would see the "sacrifice" as a human sacrifice which is explicitly forbidden by the law. Secondly, the concept of a perfect sacrifice that serves as eternal expiation is also disavowed by Judaism.