If you want to listen to what Tim Keller does when he holds Open Forums for non-Christians, skeptics, seekers, etc...listen to "Losing My Religion: Why Christians Should Drop Their Religion." Redeemer has audio from 44 Open Forums, though I haven't checked if audio for others is offered free like this one. MP3s are typically $2.50, but this one is free.
I listened today. Instructive for us as missionaries and preachers, evangelists and apologists, disciples and strugglers with religiosity. He confronts religion, truths, psychology, philosophy, and truth-claims respectfully, yet still directly.
How can we as pastors and ministers speak to our city, our culture, with intellect, wisdom, courage, and charity? Keller's example helps me, and I hope it will help you too.