I've had this conversation with some people and I think I posted about it a few times. Basically where does morality come from? Is it always based in religion or something else? Is our basis of law based in religion? Etc.
Well, I was poking around and came across a transcript of a debate between a well known atheist and a well known pastor. Some really good questions are presented from both sides and it is really a fascinating conversation.
In any case, regarding the topic of this post, I'm going to link to page 4 of the transcript where they are talking about morality and it's source. Check it out and, if you are really bored, read the whole thing! :)