"Church planting should not be like building a building-one big traumatic hiccup and we are glad that's over with."
Rather, Tim Keller argues that church planting after the biblical model of Paul's ministry should be a regular part of church existence and growth. Evangelism, discipleship, and church planting are the "Natural Church Planting" model according to Keller.
He has several insightful articles on the topic here.
(HT: Steve McCoy's list)