A good article from USA Today called Has the notion of sin been lost? interviews a wide range of preachers from Tim Keller and Mark Driscoll to Al Mohler and Michael Horton to Pope Benedict and Joel Osteen.
It ends with this definition of sin from Driscoll: "anything contrary to God's will. People assume the way they are is normal, not that something has gone terribly wrong, and this world is abnormal."
...Driscoll is sharply clear:
"Without an idea of sin, Easter is meaningless."