I'm re-listening through some of Keller's online sermons and talks. You can find them on my Tim Keller Resources page. Whether you are pastoring (like me), planting a church or a church leader, Tim Keller's talk on church planting, "Why to Plant Churches," is very helpful. I really like how he explains the value of new churches, not only as a way of effective evangelism, but also as a way to strengthen established churches in the area. Check it out.