One thing that Christianity brings to the table morally is the existence of commandments that humans have broken. While everyone has their own definition of morality, the existence of a commandment (as opposed to, say, the Ten Suggestions) seems to suggest that this is something that human beings have to do whether they like it or not or whether they agree with it or not. So if, let's say, the President of the United States has a problem accepting the commandment not to commit adultery (I think this actually happened a few years back), if he believes in a God who gives commandments, he cannot reasonably say that his opinion of adultery is as legitimate as God's. This seems to suggest that Christianity is committed to the idea of an objective right and wrong.
This point seems to be lost on some Christians, who when questioned in polling a few years back, accepted moral relativism.
There is, of course, the further question of whether being commanded by God is what it is for an act to be moral. One possibility is this: God makes humans in such a way that they will be happy (or perhaps, happy for an eternity) only if they behave in certain ways, and then God commands what is going to be conducive to human eternal happiness. If that were true, then being commanded, by itself, doesn't create rightness.
The other point to make is that commandments are not going to settle all of the debatable philosophical issues. The Sixth Commandment says "Thou shalt not commit murder." But that leaves the question of whether, capital punishment, war, or abortion are in fact murders. Since murder is definable as intentional homicide without moral justification, the question is still open for debate as to whether capital punishment and war have moral justifications, or whether abortions (or some of them) are homicides. (I'm not saying there's no correct answer to these questions, but you have to examine the pros and cons on these issues to reach a conclusion).